Does artificial high intensity light damage permanently dark ecosystems?

Does artificial high intensity light damage permanently dark ecosystems?

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Popular science features on wildlife typically capture camera images using natural light, or high-speed exposures. This is not possible where the ambient light is extremely poor. E.g. Caves, Undersea

For beings accustomed to the stygian dark, the high illumination for a video camera and/or the flash of a still camera could both be the equivalent of a 1" spanner wallop on the head or worse. Do we, inadvertently, injure the local ecosystem this way?

I don't know how harmful the exposure to a camera flash could be to organisms that live in complete darkness. However, since the animals that live in this conditions are usually blind, and the time of exposure is quite short, it's reasonable to assume that the damage produced should be minimal.

In the case of caves, permanent artificial illumination is very destructive to the environment, but the effect is due mainly to temperature changes and the introduction of organisms coming from more illuminated parts of the cave (cave organisms are usually slow and react poorly to light, so they are an easy prey if they're under light). In fact, for tourist activity, the use of lanterns or miner helmets is highly recommended.

In the case of abyssal ecosystems, ecological invasions are less likely, since there still exist a vertical barrier based in temperature, oxygen and carbon dioxide concentration and pressure. However, in this ecosystems there exist many animals which are very sensitive to light, due to the prominence of bioluminescence. Some of this animals could be damaged by the kind of light you describe. However, it's very unlikely that the main functioning of this ecosystems could be affected because of its extensive size. Moreover, the low population densities it has implies that even very long submersions would encounter only a few samples (with the exception of volcanic vents and some other geological curiosities which, in fact, are even more isolated from the rest of the biosphere by physical and chemical barriers), so the global effect should be negligible.

Yes, it's possible to damage dark-adapted ecosystems this way, and there are at least a few examples of it happening:

  • Deep sea Norwegian Lobsters were blinded by being brought to the surface as bycatch by fishermen (or by scientists tagging them). The original paper is Loew 1976, a more recent paper (Chapman et al. 2000) suggests that even a <1 minute light exposure could cause significant harm, which suggests a camera flash could certainly have an effect.
  • There is evidence that shrimp that live by deep-sea hydrothermal vents have been blinded by the floodlights of exploratory vehicles (Herring et al. 1999).

Chapman, CJ et al. (2000). Survival and growth of the Norway lobster Nephrops norvegicus in relation to light-induced eye damage. Marine Biology 136:233-241 doi:10.1007/s002270050681

Herring, PJ et al. (1999). Are vent shrimps blinded by science? Nature 398:116 doi:10.1038/18142

Loew, ER (1976). Light, and Photoreceptor Degeneration in the Norway Lobster, Nephrops norvegicus (L.) Proceedings of the Royal Society of London. Series B, Biological Sciences 193:31-44

Lighting Systems


Plants are the only organisms capable of the amazing feat called photosynthesis , by which carbon dioxide and water are converted into carbohydrates using light. Light from the sun, or other sources runs the greenhouse. Greenhouse should provide a space with optimal conditions (light, temperature, nutrition, pest control, etc.) for the plants so that they can perform photosynthesis. Often, natural sunlight is enough, and can be even too intense for some plants in terms of light but also in terms of temperature. Because the sun reflects through the glass of the greenhouse, the temperature can increase drastically and be above the temperature required for the plants. In those cases of excess light from the sun, shading or cooling by other means is required. Greenhouse mechanical cooling sytems (ventilation, etc.) are obviously important in this regard and will be discussed in Chapter 6. However, reducing light levels to control temperature is a task that should be studied carefully for example, mechanical cooling may be better option for plant growth than reducing light so that plants are not suffering from lack of light. Actually, one of the most important challenge of a greenhouse managers will be to provide plants with enough sunlight to grow them optimally. This is particularly true in North temperate locations like the North Eastern or North Western US, where cloud cover during the winter months does not provide plants with optimal light for photosynthesis. Therefore, under these conditions, supplemental lighting is usually required.

The first part (I) of this chapter will deal with some of the light-related terminology used in greenhouse management, followed by a section on solar radiation (II), and on the different types of artificial/supplemental lighting sources (III), and finally a section (IV) on shading in the greenhouse. "

I. Light: its involvment in plant developemnt and its terminology.

I. A. Importance of light

In greenhouses, managers are facing two situations in terms of lighting:
1- the light intensity is low and in that case supplemental lighting should be choosen judiciously, or
2- the lighting intensity is too high for the well being of the plants, then it will be necessary to find a way to reduce light intensity so that the conditions are optimal for plant growth.
Light is an essential element for the plant because it controlled numerous events in plant growth developemnt including plant form and structure ( morphology ), plant orientation ( phototropism ), and reproduction ( flowering ).

Light is indirectly involved in transpiration (or water loss) from leaves. Early morning, light is the trigger that causes opening of the tiny pores on the leaf surface known as stomates . Opening of stomates, in response to light, allows gas exchange between the plant and the external environment. The process of photosynthesis depends on uptake of CO2 through open stomates. At the same time, that CO2 is being taken up, water vapor is being lost from the leaf through the process known as transpiration.
Actually, light is one of the component that should be highly controlled so that it does not participate to the overheating of the leaf, which would lead to excessive transpiration of the leaves. But the light environment should be controlled in association with temperature.

S ome plants, called photoperiodic plants, are sensitive to photoperiodism, the duration of day-night Photoperiodism is a biological response to a change in the proportions of light and dark in a 24-hour daily cycle. Plant can be grouped in three categories with respect to how their flowering pattern responds to day length.
Some plants are short-day plants like chrysanthemum, Christmas cactus, and poinsettia. They flower naturally (outdoors) in the fall, when the daylength (photoperiod) is shorter than some critical length (different for different species). Long-day plants like rudbeckia and California poppy normally flower outdoors in the summer, when light duration is longer than the critical length. Day-neutral plants like rose and tomato cultivars flower without respect to day length. Artificial manipulation of photoperiod of short and long day species in the greenhouse environment allows these species to be flowered at any time of year.

John Kumpfsays on photoperiodism:

"Learning how to manage the light environment in the greenhouse will help you to maximize plant growth (photosynthesis), initiate or delay flowering (photoperiodism), avoid excessive stretching/elongation ( etiolation ), associated with low light, and avoid plant stress (which inhibits growth) associated with overheating and excessive waterloss (transpiration). Broadly speaking, these responses to light are controlled by managing the brightness of light (intensity or illuminance) and/or the duration of light (daylength or photoperiod).."

I. B. Light terminology

When the greenhouse manager needs to decide on the type and the amount of lighting required for his/her plants, it is important to be familiar with light terminology so that light recommandations can be accurately interpreted.

1. Wavelength refers to the color (and energy level) of light. Wavelenth is measured in nanometers (nm) which is one billionth of a meter ( rainbow ).

2 . Light, expressed in quantity, can be either consider as 1-photometric ( luminous flux or illuminance ) or 2-radiometric ( irradiance or luminous efficacy ).

3. Plant's energy requirement can be expressed as irradiance. The units are milliwatts per square meter or milliwatts per square foot (mW/m2, mW/ft2). This represents the quantity of energy received by a plant in the wavelength band 400-700 nm. However, foot candle are readily used, it is actually easier to evaluate lighting levels in foot-candles and to convert it to mW/ft2 using a conversion factor which is different depending on the type of lamp used.

4 . Light measurement reflects three basic quantities:
- Luminous intensity represents the total output of light source and is measured in candela usually given by the lamp manufacturer. The luminous intensity provides the weighting factor needed to convert between radiometric and photometric measurements.
- Luminance or brightness refers to light that a surface emits. Measured in foot-lamberts, luminance of surfaces depends on their visual appearance ie if they are dark ir bright. Furthermore, the apparent brightness decreases as you go further from the surface.
- Illumination of a surface can also be measured and represents the amount of light that fall on a unit area. This is expressed in foot-candle. This value is commonly found for artificial light on plants.
Usually a photometer, also refered as light meter, is the instrument used to measure illumination.

5. Horticulturists estimate the instantaneous light level using the number of micromoles of photons in the PAR spectrum that reach one square meter each second ( This represents the light energy used in photosynthesis. A measurement in micromoles actually describes the amount of usable light energy that a plant receive for growth. The PAR can be measured using a PAR meter.

II. A. Definition of the components of radiation.

Radiation from the sun can be described quantitatively or qualitatively.
The waveband of the light, as well as the distribution and intensity of the wavelengths within the waveband will determine the quality of the radiation received by the greenhouse.
The quantity of the radiation corresponds to the amount of energy within the radiation. This energy is quantified by the number of photons of light [moles of photons] per square meter per second, µmol m-2 s-1, or as a total energy value of the light, Watts per square meter [W m-2].
The wavelength or its frequency is another means to describe the radiation.The wavelength is typically expressed in nanometers (nm) or micrometers (µm) whereas the frequency can be defined as units of cycles per second,
Wavelength and frequency have an inverse relationship: as the wavelength increases, the energy of the light wave decreases, and on the contrary, as the wavelength decreases, its energy increases.

II. B. the different wavebands of interest in the radiation spectrum

The solar radiation can be divided into three wavebands:
- the ultra -violet (UV) corresponds to the wavelengths less than 400 nm and can cause skin damage because of their high energy.
- the visible light, within the 380-770 nm waveband, and contains the PAR (400-700 nm) waveband.
The different colors of the visible light, which corresponds to different waveband, may not have the same function towards plant's development.
For instance green (495-566nm) and yellow (566-589nm) light contributes to photosynthesis, orange (589-627 nm) will optimize for maximum photosynthesis and red light (627-770 nm) enhances flowering, stem elongation.
- the infrared (IR), greater than 770 nm and have an heating effect. Red: Far-red (R:FR) ratio is very important for plants because it influences plant growth response

The leaf is designed to absorb nearly 95% of wavelengths between 400 – 700 nm, but only 5% of the 700-850 nm waveband is absorbed. Of the remaining 95% of the 700-850 nm waveband,

45% is reflected, and 45% is transmitted.

II. C. Sensors used to measure solar radiation

To measure the solar radiation, several sensors are available:
-pyranometer sensors measure the entire waveband from 280 to 2,800 nm
- quantum sensors only measure the PAR waveband ( 400-700 nm)
- spectroradiometers will measure soectral irradiance: it will measure the irradiance of photon in different wavelength that would have been previously splitted.
-to evaluate energy in the greenhouse, a net radiometer can be used: it measures the difference between the radiation that arrive from above and the radiation that is reflected from below.

II. D. Solar radiation and greenhouse

Greenhouse structures are an obstacle for solar radiation: frames, glazing bars, dirt, gutters, because they are opaque, absorb or reflect al the light that reaches them. Numerous greenhouse equipment are blocking the light from reaching the plant inside. In conclusion, a large portion of the solar radiation ( between 30 -50%) does not reach plants. The greenhouse cover, plastic or glass, will also have an important impact on light transmission.

Plant growth of plant can be manipulated with solar radiation. Current methods to regulate plant growth in the greenhouse may include daily exposure of seedlings to red or far red lighting at the end of the day for several weeks prior transplanting in the field. This treatment will alter the plant height and the total leaf area.

A daily cool-white lighting for several weeks for one hour before the end of the natural photoperiod will also alter plant height and total leaf area.

To reduce plant height, Far Red can be suppressed from the solar radiation using liquid copper sulfate filters.

III.Artificial Supplemental Lighting in the greenhouse

Supplemental lighting, to increase illuminance and/or to extend photoperiod can be a significant portion of the total greenhouse energy use. In addition to the investment in the lighting system itself, it is important to choose the most economical light source to fit the needs of the plants. All types of lamps convert electrical energy into both light and heat. Different kinds of lamps differ in the efficiency of their conversion of electrical energy into light . This affects not only the greenhouse energy budget in terms of the cost of electricity, but also in terms of dealing with the "waste heat" generated by the bulb. This can either contribute in a positive way to heating the greenhouse during the winter, or in a negative way if "waste" heat generated by the lamps increases the demand on greenhouse cooling systems (shade and/or mechanical systems)

III. A. Incandescent light bulbs.

Anyone who has ever touched a hot incandescent light bulb has experienced the fact that they are very inefficient in converting electricity into light. Hence they are not a good (economical) source of greenhouse supplental lighting when the objective is to increase light intensity. On the other hand, to control plant photoperiodic responses it requires only very low intensity to extend the photoperiod. For this purpose low wattage incandescent lighting may be a good way to inexpensively increase day length.

Some characteristics of incandescent lighting includes:

-Good source of red wavelengths
-Poor source of blue wavelengths
-Too hot for most plants, unless placed at least 3 feet above the plants.
- Easy to install
- One-third as efficient as fluorescent tubes
-Bulb's life is often only about 1,000 hours.

Incandescent Light With Aluminum Reflector can be used to redirect the light emitted by incandescent bulbs in order to increase their efficiency (brightness).

John Kumpf on Installation of Incandescent Lighting

John Kumpfsays on Installation of Incandescent Lighting :

"Installation of incandescent lights is the easiest of all the lighting fixtures. Incandescent lights over plant material in the greenhouse often ends up being permanent even though that may not be the original intent. Ease of installation makes incandescent lighting especially popular for the small grower looking to control photoperiod. When installing this type of lighting be sure to use the proper size wire. To use the proper size wire, check local codes at any electrical outlet store in your location. Coated #12 solid copper wire works best. To connect the light to the wire use a screw on weather proof socket , making sure good contact has been made between the socket and the wire. The wire should be supported by structures that are free from sharp edges. They should always be wrapped around insulators rather than wood or piping. Also, be sure to tape any exposed ends. Sunlight can break down the coating on the wire, be sure to inspect the wire and all fixtures on a regular basis."

III. B. Fluorescent Lighting

Florescent lights are more efficient than incandescent lights in converting electricity into light, so they don't generate as much waste heat and their fixatures are cumbersome. However, incandescent, are limited in how much light intensity they can provide, take up a lot of space, and they are expensive. The wavelength distribution (color spectrum) of standard (cool white) florescent lamps is high in blue but low in red. Modified spectrum florescent lamps are available which are enriched in the red wavelengths so the overall spectrum more closely approximates that of sunlight (e.g. Grolux, Plant-Gro, and Optima). The downside of this modification is that it decreases overall light intensity. The advantage gained by the modified blue-red spectrum is more than offset by the loss of intensity and their increased price. Overall a grower is better off using standard cool white floresencent bulbs particularly when florescents are used in combination with incandescent (red rich) lighting or when florescents are used to supplement natural lighting which provides plenty of red light. Florescent lighting systems not generally used for supplemental greenhouse lighting when increased light intensity is the goal. Instead, they are primarily used in growth rooms or short term germination areas, either alone or in combination with incandescent lights.

Fluorescent tube's life is normally 10,000 hours or more and energy efficiency is 40-60 lumens/watt.

John Kumpf on Installation of Fluorescent Lighting

"Fluorescent lighting is generally used in greenhouse only when low natural light is available. More often, fluorescent lights are used in propagating areas or growth room that receive no natural light.
Remembering that fluorescent light intensity weather it "very high output" or "high output" decreases dramatically as the distance from the plant increases. The support structures are usually designed to keep fixtures relatively close to plants ( i.e. 6 through 24 inches). Fluorescent light tubes are the lite part of the equation whereas the hallasts and reflectors can amount to substantial weight. The lights can be hung with boiler chain and shooks from constructed wood or pipe frames located over the bench. Donn't hang the fixture from the sash bars. In some situations, the reflectors can support the weight of the fixtures, however, this requires several cross stringer because most fixtures are no more than 8 foot long. As with any type of electrical set up, wether temporary or permanent, be sure on checking local wiring codes."

C. High Intensity Discharge (HID)

HID lamps are the most efficient at converting electricity into light and for this reason they are the most economical for greenhouse supplemental lighting when the primary goal is to increase light intensity.

There are two types of HID lamps - high pressure sodium (HPS) and Metal Halide (MH):

a). High Pressures Sodium (HPS) - these are the orangish lights you see illuminating shopping center parking lights. Their spectrum is rich in red wavelengths that provide an effect on daylength perception in plants, hence promoting both growth and flowering in long-day and day neutral plants including annuals. But this spectrum is comparatively poor in blues. They are used for supplementing lighting because they are efficient at converting electrical energy into PAR light (20-25%), and are available in high voltage. Bulb life is usually around 25,000 hours.

b). Metal Halide (MH). Most commonly used by professional greenhouse growers because their spectrum is more balanced than HPS. Because it provides more blue light than orange/yellow, and because plants are less disturbed under MH settings, these fixtures are mostly used for displaying plants in retails settings.

John Kumpf on HID Lamps

"These high pressure sodium lights are 400 watt lamps over some tomato plants in the greenhouse when you look at these one of the things you look for is light uniformity over the plant material and they should be setup on specific grids so that you have uniform light over the entire greenhouse. If you don't, you're going to have variations in how the plant material responds to the amount of light that the plant is receiving. Those that receive less light may be along the outside of the benches and will etiolate (stretch). So check the configurations of your lamps to make sure that you have good uniform lighting over all the plant material.

Be aware that light uniformity is extremely important when manipulating the light intensity in the greenhouse. In this particular situation we're not talking about photoperiod control, but we're talking about the available light that the plant has which in turn relates to photosynthesis. Looking at these lamps you notice that they are approximately 4 feet up off the top of the plant material. Pay attention to the distance between the light bulb and the growing point of the plant, it is essential to learn how close the plant can get before the heat and Hi light impact its gorwth. These are tomato plants and they are very sensitive to the heat, so we elevated the lights up off the plants and increased the number of lamps. This way we get the correct light intensity and uniform distribution. We also put white plastic down on the floor or paint the floor white to reflect light back up.

These lamps are set up to increase light intensity and they are used to extend the day length. Normally we would run these 18 hours a day from 6 in the morning until midnight, extending the day length to increase production. Whether it is tomato plants or roses, these lights do increase the growth and production in the winter time. We turn the lights off on April 15th and don't turn them back on until the 15th of October.

These are low profile luminaries. You want to make sure you clean the insides of these well. Take a piece cheese cloth and wipe them out before you put them up. This will ensure the most reflective light. So clean the inside of the lamp also take the outside of the lamp and rub them down as well, we want to keep these so that they will give you as much as reflected light as possible."

John Kumpf on Installation of HIDs

"High pressure sodium and metal halide fixtures are not easy to install and should be considered a permanent installation. The process requires two people, ladders tall enough to eliminate any excessive reaching, the proper weight chain, and hooks strong enough to hold the weight of the fixtures. I do not recommend hanging the lights from greenhouse sash bars because the accumulated weight of several lamps could damage the bars. The best way is to hang the lamps from sturdy interior structures or construct a grid out of heavy duty channel iron.

All wiring should be done by a qualified electrician. I would pay attention to the lay out of the electrical circuits which determines what lights are on or off. The importance of this reverts back to how much of the greenhouse will be lit at one time."

Example of calculation to determine fixtures location:

- A grower has a 9' x 128' bench over which he wants to suspend HID lamps of 400W.
- The light intensity desired for the plants that he is growing is 8600 lux or 800 fc. The effective flux of the HID lamps is 38,400 lumens.
-The number of fixtures (N) is calculated using this formula:
N = (light level x surface area)/ effective flux.
-For the grower in question the number of fixtures is then 24 [(800 x 9 x 128)/ 38,400].
- The pattern of those fixtures is defined as the horizontal spacing and the height above the crop surface. For each lamp the distance between fixtures along the line (L) and the distance between lines (B) is usually given. You can refer to Poot (1984) to find out those numbers.
In our example L = 1.55H and B = 2.7H with H the height.
Since Light level (E) = Effective flux (F)/ area (A)
A = L x B = 1.55H x 2.7H = 4.2 H2.
Therefore, H = racine carre of (A/4.2) = 3.38 ft
and L = 1.55 x H = 5.24 feet
and B = 2.7 x H = 9.13 feet

IV. Reflectors

Uniform distribution of light is of importance for crop production in greenhouses. A lighting system depends strongly on the way light is distributed across the crops. The secret to obtaining a uniform blanket of light is to equip light fixtures with reflectors, which receive and reflect light in the desired direction. Its shape, reflecting angle and the emission of total light quantity between that angle determine the efficiency of each reflector.

The goal of using shade to grow crops is to reduce the amount of sunlight reaching a crop so that stress on plants caused by excessively high temperatures can be reduced. The use of shade is also an important way to reduce the temperature of the plants. The greenhouse manager needs to decide if light should be reduced to achieve temperature.

Greenhouse shading can be done using one of two methods: 1-either an external application of shading compound, 2- internally using a woven type of shading fabric. External shading is most effective in decreasing heat buildup in the greenhouse. However, applying a uniform coating of shade is difficult, as is removal, and once the shade is applied, it is semipermanent. Furthermore, cloudy days even during the summer means that plants may be receiving insufficient light for a long period of time. The problem of permanence can be overcome using internal shade, since shade material can be pulled and withdrawn as needed. However, the cost of internal shading is high and it does not prevent light from entering the greenhouse and then from being converted to heat. But using reflective or white material can reduce the problem.

John Kumpf on Shading

"Shading is a step in greenhouse management that should be done very cautionely, especially permantent shading. Shading has two main effects in greenhouse: it reduces the temperature and the light intensity. THerfore it is important to consider both factors when decide which shading technique to utilizes. For example if shading is used to decrease temperature in greenhouse, it will also decrease the light intensity that plants in the greenhouse will receive. And this may affect their growth. Therefore it is important to find a balance between light and temperature when it comes to install shading.
Shading plants in greenhouse varies considerably from small to large greenhouse.
Shade curtains in a large greenhouses often serve two purposes: reduce light in the summer and act as a thermal blanket in the winter. Modern shade screens can drastically change the greenhouse environment. They can be used to control temperature , reduce energy costs, and help cut down on the amount of water taken up by the plant to say nothing about creating a more comfortable environment for the greenhouse worker. Manual or computer controls activate the curtain giving the plant material growing under it the proper amount of light. Computer programs can control shade curtains so the plant gets just the right amount of light. When intensity is too high, the curtain closes and vice versa. Furthermore, those programs can also estimate the amount of light a plant will receive based on the accumulated light of the first few hours of the day determining whether the curtain should remain opened or should be closed. Always remember to install a manual over ride on this equipment. PICTURE.
Small greenhouses often use manual methods of shading plants. PICTURE The support structures for shade cloths in smaller greenhouse is usually a wire heavy enough (14 - 12 GagueA.).PICTURE
This wire is run from supports at each end of the bench and the sahde cloth is pulled on the plants. The same cloth can be used to control photoperiod. Using the greenhouse catalog, select the best material to serve the purpose, many different quality are available and this quality will modify the percentage of light reduction.
When you are finished using shade cloths be sure to take it down. It collects dust and can also fade, changing its light transmission reducing characteristics.
Shading Compound is one of the most famous external manner to control glass or polyethylene greenhouse shading. Shading compounds will diffuse light rays and reflect heat. If used with material other than glass, the shading compounds may harm the glazing and may not be easy to remove if not possible at all. Shading compounds come either in white or green and can be thinned using paint solvent. They are extremely effective in decreasing heat buildup in the greenhouse. However, it is difficult to apply and to remove the uniform coating of those shading compounds. Once applied, the shade is semipermanent, and during cloudy and dark days of summer, the plants in the greenhouse may receive insufficient light for several days. The second method to reduce light level is to block out light with some shading screens made of cloth, polypropylene, polyester or aluminum-coated polyester. These systems may be placed on the exterior of the greenhouse or on the interior .
When associated with cloth moving devices, movable black cloth will then offer some control of the greenhouse temperature. However, it is not always recommanded to utilize black cloth because it always increase the temperature because it ablsorbs light. It is also important to use good fan ventilation.
Used to control photoperiod, and especially to provide short day-light period. Cloth is pulled over the plants at 5pm and taken off at 8am. The cost runs 4 - 5 dollars per yard and comes in increments of 5' wide by any lengths. Extreme care should be taken when handling and setting up black cloth. Always make sure that cloth is in good shape (no holes and not faded). Any holes in the cloth should be repaired immediately because any external light reaching the covered plant material can cause delays in flowering as well as uneven flower bud initiation. Go over pinning to make sure that all holes are covered.
Also, don't leave cloth up after it has been used because sunlight will fade it when pulling the cloth shut. The area of most concern should be where the two cloths come together. Whether they are pinned together or one on top of the other, particular attention should be paid to this area. Be sure that all sharp edges are eliminated on the wire that the cloth is pulled over. Be sure that the wire is heavy enough to support the cloth, especially if your greenhouse has leaks that allow water to drip on the cloth. This should be avoided because water can cause the cloth to sag causing injury to the plants underneath."

Saran or polypropylene is used to reduce light over plants, especially when newly potted or recent cuttings. Comes in varying degrees of shade from 20% - 80% light reduction. Polypropylene film is used to reduce light over plants, especially when newly potted or recent cuttings. Black polypropylene is used to construct the shading cloth manufactured for today's greenhouses. This material is very strong and has a high U.V. protection. The grower has a wide range of shade percentages to choose from depending on their situation. A 30 - 95 percent shade cloth can be purchased. There are many links to commercial supplies of polypropylene film that will show the range of options available.

(Put in question here and at other question mark icons? Suggest using the links we have provided and any other **reputable** (define?) info they have access to in order to answer the question or develop some kind of strategy. Sort of interactive, not so passive?)

The information in this Web page is presented with the understanding that no discrimination or endorsment of any of the information linked to from this Web page is implied.

Why conservation biology can benefit from sensory ecology

Global expansion of human activities is associated with the introduction of novel stimuli, such as anthropogenic noise, artificial lights and chemical agents. Progress in documenting the ecological effects of sensory pollutants is weakened by sparse knowledge of the mechanisms underlying these effects. This severely limits our capacity to devise mitigation measures. Here, we integrate knowledge of animal sensory ecology, physiology and life history to articulate three perceptual mechanisms—masking, distracting and misleading—that clearly explain how and why anthropogenic sensory pollutants impact organisms. We then link these three mechanisms to ecological consequences and discuss their implications for conservation. We argue that this framework can reveal the presence of ‘sensory danger zones’, hotspots of conservation concern where sensory pollutants overlap in space and time with an organism’s activity, and foster development of strategic interventions to mitigate the impact of sensory pollutants. Future research that applies this framework will provide critical insight to preserve the natural sensory world.

Human activities are affecting life on our planet at an unprecedented rate 1 . In the last century, there has been tremendous growth in transportation networks, urban land cover and intensive farming 2 . This spectacular level of expansion has heavily relied on technological advancements in engineering, physics and biochemistry 1 , but has brought along ecological consequences, such as habitat destruction, biodiversity loss and climate change 3 . An often overlooked, yet important, consequence of global human expansion is the negative impact on the sensory systems of many organisms, a phenomenon known as sensory pollution 4 . Animals rely on sensory systems (for example, their hearing, vision, smell or electro-perception) to process (a)biotic information on the physical and temporal structure of their environment. The ability to use such environmental information is critical to many ecological processes such as habitat selection, species recognition, foraging efficiency and risk assessment. Human activities interfere with these sensory systems by introducing novel chemical and physical stimuli in the environment. Among known anthropogenic sensory pollutants, acoustic noise, night lighting and chemical agents are globally pervasive, yet still rapidly growing in extent and intensity 5,6,7,8,9 . These pollutants can fundamentally impact ecological processes by altering how animals process information in their environment 5,6,10 . Sensory pollution has, therefore, been suggested to have led to population-level declines of several species, including locally and globally threatened species 11,12,13,14 , and thus poses a substantial threat to the long-term persistence of animal populations and functioning of natural ecosystems.

ALAN and the Light Environment

Understanding how ALAN affects the natural light-dark regime and how animals perceive these changes is fundamental to linking individual and population responses to ALAN with community and ecosystem processes. Sanders and Gaston (2018) categorize light (and the absence of light) based on how an organism uses light: (i) as a resource, and (ii) as a source of information. Light as a resource contributes to photosynthesis and primary production in the aquatic environment (reviewed in Kirk 2011). Animals perceive information from light in various ways, which requires light-sensitive photoreceptors. The detection and neural processing of variability in the light environment can inform scotopic (dim-light) and photopic (color) vision, spatial orientation, and biological rhythms (including circadian, migratory, and reproductive cycles). In this section, we provide an overview of light in the environment, how it is detected and used by animals with an emphasis on estuarine communities, and how ALAN alters the natural lightscape. We briefly outline how animals detect light and then offer several relevant examples of ways in which animals utilize light as an information source.

The Estuarine Lightscape

Light environments are determined by the cyclical nature of light intensity and spectral patterns and by the way that light moves through air and water. The timing and duration of light-dark cycles throughout the day and year have been predictable cues for organisms through evolutionary time, until the last century when ALAN was introduced. The predictable nature of the transition from light to dark on daily and seasonal time scales has favored the evolution of light-detection mechanisms coupled with behavioral and physiological shifts (e.g., diel migration in invertebrates [zooplankton, Moore et al. 1998], melatonin production and decreased activity in diurnal fish [Ouyang et al. 2018]). However, at a given time and environment, the nature of light is largely determined by the absorption and scattering of down-welling light moving through the medium (e.g., air or water), and light reflecting from a surface (Lythgoe 1979). This dynamic of predictable light cycles and variation in the intensity and color of light at a given time and place creates complex lightscapes with which organisms must contend.

Light at the air-water interface is critical in linking terrestrial and aquatic biota. In air, light is scattered and absorbed by particulates ranging from water molecules to dust particles, resulting in variable sky colors (Lythgoe 1979). Structurally complex terrestrial environments, such as forested riparian zones, further filter certain wavelengths of light so that the amount and color of light reaching the water surface is much reduced (Endler 1993). Light is then either reflected into the air or penetrates the water surface and is refracted. Animals living and foraging at the air-water interface exhibit numerous adaptations to this complex lighting environment. For example, wading birds must have sufficient visual acuity to find their prey through this air-water interface, while avoiding being detected by their fish prey looking up through the interface. Green and Leberg (2005) found that white plumage color in snowy egret (Egretta thula) and little blue heron (E. caerulea) was more cryptic than dark plumage in open intertidal zones based on the response of their preferred prey (crayfish, Procambarus spp., western mosquitofish, Gambusia affinis). This advantage disappeared when the birds were viewed against a vegetated background.

Underwater, selective absorption of wavelengths by suspended particulates influences irradiance (i.e., radiant flux received by a surface per unit area) at different water depths and depending on particulate shape and size (Loew and McFarland 1990). In shallow coastal waters, the photic environment is dominated by medium-to-short wavelengths of light, producing the blue-green color typical of these zones. In organic-rich brackish and freshwaters, dissolved organic carbon (DOC) creates a red-shifted (dominated by longer wavelengths) and less-intense (darker) photic environment (Lythgoe 1979). Additionally, turbidity derived from suspended silt, phytoplankton, detritus, and other particulate and dissolved materials (e.g., colored dissolved organic matter [CDOM]) determines the spectral absorption and scattering properties of coastal surface waters (Cannizzaro et al. 2013). Spectral absorption by phytoplankton and detritus can determine the light field of aquatic habitats just as a forest canopy filters light that permeates into the understory (Endler 1990). For example, in the subtropical Pearl River estuary of China, spectral absorbance by non-algal particulates was more important than within the inner river plume, where terrestrial detritus from runoff dominates the visual scene (Cao et al. 2003) and further, algal particulate absorption was found to be more important to spectral absorbance in more saline coastal habitats. Similarly, in a subtropical Florida estuary, shorter wavelength ultraviolet (UV) light is more readily absorbed by CDOM in the upper estuary compared to downstream (Chen et al. 2015), contributing to a red-shifted light environment in the upper estuary. Light attenuation related to this turbidity “filter” can further drive the distribution and productivity of phytoplankton, benthic algae, macrophytes (Burford et al. 2012, Cloern et al. 2014, Radabaugh et al. 2014), and potentially higher trophic-level consumers.

Light as Information

Given the predictable nature of light cycles, animals have evolved a variety of mechanisms for detecting and interpreting variation in the intensity (and in many cases, color) and direction of light. Key to light detection are photoreceptors, which can be found in the retinae of animal eyes, but also in the integument and internal organs (e.g., pineal gland of non-mammalian vertebrates). Evolutionary adaptations in visual physiology—spectral sensitivity, visual orientation, and circadian functioning—are examples of how ambient light can function as a selective pressure for estuarine animals. By changing the color (or spectral qualities), duration, and relative orientation of down-welling and polarized light in the nocturnal environment, ALAN is expected to disrupt these basic mechanisms and natural ecological functioning in estuaries.

Light Detection

Animal visual systems are composed of light-sensitive progenitor cells and photoreceptors that evolved in response to the spectral qualities of the photic environment (Lythgoe 1979). As such, the ability to detect different light intensities and wavelengths varies among individuals and species that inhabit distinct light environments (Cronin et al. 2014). For example, freshwater threespine stickleback (Gasterosteus aculeatus) exhibited differences in visual sensitivity important for mate selection in clear versus tannin-stained lakes (Boughman 2001). Studying the spectral qualities of terrestrial light environments has also informed our understanding of diurnal visual ecology, and specifically how color vision is integral in detection of food and prey resources, mates and competitors, and potential threats (Endler 1993). Spatial and temporal niche partitioning have led to the evolution of visual sensory systems in invertebrates, birds, and fishes that are specialized for performance in different light environments (e.g., habitat or time of day Cronin et al. 2014). For example, the eyes of nocturnal fish species are generally characterized by a larger lens and pupil diameter that enhance light sensitivity, dim-light image formation, and spatial resolution, but sacrifice depth of focus and accommodative lens movement (Schmitz and Wainwright 2011). Similar optical traits are observed in nocturnal shorebirds (Rojas et al. 1999a, Thomas et al. 2006). In addition to temporal partitioning of resources, the variables that influence the underwater visual environments described above, such as turbidity or dissolved organic matter, can be strong drivers of the evolution of animal visual systems. Some estuarine fish species, such as the flathead grey mullet (Mugil cephalus), living in waters with high suspended-sediment loads and associated lower ambient light levels, also exhibit morphological traits (e.g., high rod density in the retina) that support scotopic (dim-light) vision. Euryhaline and diadromous fishes tend to have mixed photopigment systems that allow them to adapt to varying light environments encountered throughout their life histories (Toyama et al. 2008).

Visual Sensitivity

The sensitivity of animal visual systems to the amount and color of light in an environment depends on the type, number, spectral characteristics, and distribution of photoreceptors in the retina (Fig. 2 Lamb et al. 2007, Lamb 2013, Le Duc and Schöneberg 2016). Visual photopigments bind with photons via opsin proteins (G protein coupled receptors) bound to an inactive form of photosensitive vitamin A-based chromophores (Wald 1935). Cone opsin classes differ in wavelength sensitivity, and multiple classes of cone opsins are required for color vision. The photopigment rhodopsin evolved in a common metazoan ancestor, and photoreceptors have evolved independently along multiple invertebrate and vertebrate lineages (Yokoyama 2008). Aquatic invertebrates exhibit a remarkable diversity of photoreceptors, deriving from ciliary (e.g., polychaete tubeworms), cnidarian (e.g., cephalopods, corals), rhabdomeric (e.g., arthropods, molluscs), and Go/RGR (e.g., scallops) opsins that vary in function (Shichida and Matsuyama 2009). Molluscs, arthropods, and vertebrates possess rhabdomeric melanopsins, which support circadian rhythms, pupillary reflex, and other non-image forming functions (Shichida and Matsuyama 2009). Rhabdomeric Gq opsins allow for color vision in arthropods (Koyanagi et al. 2008). Vertebrates possess two kinds of ciliary photoreceptors: rods (Rh1) are responsible for scotopic vision, and cones (long-wavelength sensitive, LWS short-wavelength sensitive, SWS1, SWS2 and, rhodopsin, Rh2) provide for color discrimination and visual acuity (i.e., photopic vision). Other visual opsins in vertebrates include the melanopsins and opsins of the pineal subfamily (governed by PARA, PARE, and PIN genes). Whereas humans are limited to three photoreceptor classes for color vision (e.g., red [LWS], green [Rh2], and blue [SWS]), birds and many shallow-water fishes have retained all four classes of cone visual pigments for tetrachromacy. Sabbah et al. (2013) suggest that this allows fishes to efficiently process signals in the higher spectral complexity of underwater light environments. Nocturnality in birds is associated with rod-dominated (80–90%) retinas compared to diurnal species (20–30% Le Duc and Schöneberg 2016). A similar retinal composition is present in waterbirds, such as Adelie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) Penguins that have adapted to extreme seasonal light cycles (Le Duc and Schöneberg 2016).

Estuarine fishes are known to have rhodopsin and porphyropsin photopigments, which vary in their spectral absorption properties. Light-sensitive photopigments are composed of opsin bound to an A1 chromophore to make rhodopsin (λmax = 500 nm) in marine fish or bound to an A2 chromophore to make porphyropsin (λmax = 525 nm) in freshwater fish (Toyama et al. 2008). Mixed photopigment systems that express A1 and A2 photopigments are common in freshwater, diadromous, and certain coastal-marine fishes that adapt to varying light environments throughout their life history. In these species, ratios of porphyropsin and rhodopsin are generally dependent on ambient light and spawning habitat (Toyama et al. 2008). Euryhaline fishes like a the gray snapper (Lutjanus griseus) and b common snook (Centropomus undecimalis) exhibit greater sensitivity toward longer or shorter wavelengths along the freshwater-marine gradient of an estuary. The changing proportion of these photoreceptors allows diadromous fishes to adapt to their environment during ontogenetic changes between marine and freshwater habitats (Allen and McFarland 1973, Robinson et al. 2011). ALAN implications: Artificial light spectra will theoretically stimulate the photopigments of freshwater, euryhaline, and marine fishes to varying degrees. Marine fishes are expected to be especially sensitive to light-emitting diodes (LEDs see Fig. 4 for details on intensity and wavelength), which emit high-irradiance spectra that can be readily absorbed by rhodopsin. Although low-pressure sodium (LPS) lamps are commonly used to minimize ecological impacts (e.g., disorientation of sea turtle hatchlings), certain freshwater and euryhaline fishes would still perceive this narrow-spectrum lighting (Bird et al. 2004, Davies et al. 2012). Thus, LEDs might be expected to elicit behaviors typical during daylight in some fishes. For example, Becker et al. (2013) observed that large, predatory fish were more abundant on nights when a LED light was turned on, mimicking diurnal predatory activity. Whether such short-term individual behavioral responses would be favored over time would likely depend on the consistency of exposure to ALAN and the concomitant behavioral responses of their prey. The long-term, evolutionary impacts of ALAN on visual sensitivity, further enhancing the ability of some fishes to thrive under ALAN, are not known

The ability to tune photoreceptors, either by change to the molecular configuration of opsins or expression of different opsin genes, allows aquatic animals to be more sensitive to specific wavelengths of light. Spectral tuning specifically refers to plastic or evolutionary change in peak sensitivities of visual pigments in response to the photic environment (Carleton 2009). Plasticity in opsin gene expression allows for tuning of visual pigments to different light environments (Viets et al. 2016). Evolutionary shifts in mammals and birds from nocturnal toward diurnal habits led to a loss of sensitivity to UV irradiation (Hunt et al. 2009) and increased sensitivity to longer wavelengths that correspond with crepuscular light in forests (Endler 1993). These shifts were likely adaptive in preventing retinal damage from UV exposure. In contrast, the SWS1 in gulls (Laridae) are tuned to UV (Hastad et al. 2009), which may aid foraging in highly polarized bright light. Fluidity in opsin gene expression has led to a range of sensitivities across taxa, yet certain patterns have emerged for organisms that live in aquatic environments.

480 nm) plays a primary role in non-image-forming photoreception in marine and terrestrial vertebrates as the dominant light available in deeper water (λmax, 470–490 nm Lythgoe 1979) and in terrestrial environments at crepuscular intervals (λmax, 450–500 nm Munz and McFarland 1973 Endler 1993). Circadian rhythms (also see “Biological rhythms: circadian activity levels”, below) in aquatic organisms are thought to have coevolved with blue-light photoreception (Erren et al. 2008). For example, the blue-sensitive pigment PIN expressed in the pineal gland of birds plays a role in controlling avian biorhythms. Other cases of spectral tuning have been linked to aquatic environments. For instance, expression of the RH1 opsin has undergone spectral tuning in marine mammals as related to water turbidity (Borges et al. 2015). Visual specializations (i.e., opsin gene expression and spectral tuning) associated with habitat and temporal niches are expected to result in species-specific responses to common artificial light spectra (Fig. 3). However, blue emissions, which are included in some broad-spectrum artificial lights, may influence circadian functioning in many aquatic and terrestrial organisms.

Emission spectra of four artificial lighting types including a metal halide, b light-emitting diode, c halogen, and d high-pressure sodium lamps (spectra from Lamp Spectral Power Distribution Database 2017)

Visual Orientation: Polarotaxis

Polarotaxis is the ability in some animals to orient based on the angle of the sun’s rays. Polarization sensitivity or adaptive camouflage in polarized habitats are understudied organismal responses that can have consequences for individual fitness and predator-prey interactions. For instance, polarized light can provide cues for spatial navigation and habitat selection important to animals sensitive to polarized light, such as aquatic and terrestrial insects (Boda et al. 2014, Perkin et al. 2014a), fishes (Hawryshyn 2010, Kamermans and Hawryshyn 2011, Pignatelli et al. 2011), birds (Muheim 2011), and bats (Greif et al. 2014). Polarization detection depends on the presence of a photopigment that is sensitive to either UV or short wavelength light (e.g., less than 400 nm). The freshwater crustacean Daphnia pulex exhibits sensitivity to polarized light although this ability is lacking in its congeners (Flamarique and Browman 2000), indicating that polarotaxis can be species-specific in aquatic macroinvertebrates. Polarization sensitivity can be especially important for aquatic insects active during crepuscular light intervals (Bernath et al. 2004) or inhabiting environments characterized by high UV (< 360 nm) such as clear, oceanic waters or yellow-green (550 nm) light (Schwind 1995), such as waters with dense phytoplankton growth. Polarized light created by reflective non-water surfaces (e.g., asphalt, glass) can create “ecological traps” for polarotactic insects (Horváth et al. 2009, Boda et al. 2014). For example, flying adult aquatic insects returning to water for oviposition detect the horizontal polarization of water-reflected light under natural conditions, but under ALAN are instead often attracted to urban light sources and horizontally polarizing non-water surfaces (Robertson et al. 2010).

Polarization sensitivity can allow predators to perceive prey as more conspicuous (i.e., higher contrast) in polarized habitats (Shashar et al. 2000). Some open-ocean fishes have modified reflective platelets that support polarocrypsis from predators (Brady et al. 2015). Polarization sensitivity has also been studied relative to habitat orientation by estuarine fishes—primarily salmonids and cyprinids. Species with specialized UV-sensitive SWS1 cone photoreceptors can detect cues primarily from celestial polarization that help in mapping natal stream location (Hawryshyn 2010). As migratory Pacific salmonids adapt from living in freshwater to saltwater (i.e., during smoltification), UV-sensitive cones undergo apoptosis to prevent retinal damage in clearer coastal environments but are later regenerated as mature adults migrate back upstream to natal habitat (Quinn 2004).

Biological Rhythms: Circadian Activity Levels

Temporal shifts in natural light (e.g., daily, seasonal) structure internal circadian rhythms that drive many physiological processes and behaviors of visual and light-detecting organisms. Diel patterns of light create optimal and suboptimal periods for activity by aquatic-associated animals. For example, the polarotactic detectability of water by aquatic insects (governed by solar elevation) during mid-morning, early afternoon, and dusk make these optimal periods for dispersal (Csabai et al. 2006). Furthermore, the duration of these optimal dispersal periods varies latitudinally. Changes to the “polarization sun dial” (sensu Csabai et al. 2006) induced by ALAN may have a stronger impact for aquatic insects in tropical systems where morning and evening periods are shorter.

Variability in light intensity throughout the lunar cycle directly influences foraging behavior by aquatic-associated organisms. During a full moon (Fig. 4), some nocturnal seabirds tend to forage for shorter intervals, whereas foraging activity is extended for some diurnal species (Tarlow et al. 2003, Navara and Nelson 2007). A breakdown of natural light cycles disrupted by ALAN may influence temporal niche partitioning, stemming from changes in foraging and predator-avoidance behaviors. Although here we focus on potential effects of ALAN on diel activity patterns, light also plays a key role in physiological and molecular pathways that influence seasonal breeding, migration, and orientation (reviewed in Dominoni 2015).

Emission spectra of solar (source: Lamp Spectral Power Distribution Database) and lunar light (source: From a visual perspective, ALAN increases the intensity (measured in lux or irradiance) of nocturnal light environments and shifts the spectral distribution typically to longer wavelengths (Johnsen et al. 2006, Cronin and Marshall 2011). ALAN can illuminate the nocturnal environment to intensities ranging between that of nautical twilight to brighter than a full moon on clear nights by more than 2 orders of magnitude (Kyba et al. 2011, Gaston et al. 2013, Bolton et al. 2017). Without moonlight, ALAN can exhibit peak fluxes at 560, 590, 630, and 685 nm (Johnsen et al. 2006)

The impacts of ALAN on circadian activity levels of avian consumers relate strongly to feeding strategies. Shorebirds and wading birds are resident and transient consumers in estuaries and coastal wetlands. Common taxa—such as herons, egrets, sandpipers, and plovers—vary in their visual capabilities, feeding strategies (visual or tactile), and diel activity patterns. Wading birds with weaker photopic vision capabilities (e.g., night herons and spoonbills) more often forage at night. Among the shorebirds, plovers (Pluvialis and Charadrius) and sandpipers (Scolopacidae) are cathemeral, or actively forage for periods during both day and night. Aerial insectivores such as pratincoles (Glareola) and swallows (Hirundinidae) are particularly active during crepuscular periods. Night-feeding can help meet energetic requirements and minimize encounters with diurnal predators (reviewed in McNeil and Rodríguez 1996) and while the introduction of ALAN may directly impact visually feeding shorebirds by enabling longer foraging intervals, this benefit can also extend to diurnal predators.

ALAN and the Estuarine Lightscape

The increasing intensity of ALAN, especially in coastal zones (Davies et al. 2016), is expected to disrupt natural light-dark cycles by introducing light during historically dark periods, and by providing enough light for day-active animals to see at night. The lightscape of estuarine habitats is extremely complex and thus is expected to be especially sensitive to ALAN: organismal-to-community responses to light pollution will likely vary throughout the freshwater-marine ecotone. Artificial lights can emit light in narrow or broad-spectrum bands (Fig. 3), the latter more closely mimicking natural light (Fig. 4). Davies et al. (2013) compared low- and high-pressure sodium, light-emitting diode (LED), and metal halide (MH) lamps to determine potential overlap with the visual sensitivity of arachnids, birds, insects, mammals, and reptiles to these different light spectra. Broader-spectrum emissions (e.g., high-pressure sodium, light-emitting diode, and metal halide lamps) are expected to have profound ecological effects because more species can perceive this spectral range. In particular, the increasingly popular LED lights produce broad-spectrum white light of sufficiently high intensity across the visible spectrum to allow color-mediated vision in a range of taxa from spiders to mammals (Davies and Smyth 2018). However, few comparisons of spectral perception to natural or artificial light have been drawn among riparian, freshwater, and marine taxa (Nightingale et al. 2006, Toyama et al. 2008). Building upon this approach would support theoretical understanding of physiological and behavioral responses to artificial lightscapes in estuaries. In addition, depth, turbidity, benthic substrate, and other habitat variables that define estuarine gradients may serve as useful indicators in forecasting the ecological effects of ALAN.

Consideration of the sensory environment in the context of conservation and management is an emerging field (Madliger 2012 Cooke et al. 2013 Blumstein and Berger-Tal 2015). We expect physiological and behavioral responses to the visual environment to inherently depend on the amount and spectral composition of artificial light as well as the visual sensitivity of individual organisms (Fig. 2). Growing evidence indicates that disruption to the visual environment through human-induced changes (e.g., elevated turbidity, eutrophication) leads to loss of biodiversity and alteration of communities (e.g., Seehausen et al. 1997, Seehausen et al. 2008). Our knowledge of natural nighttime light environments and communities also continues to expand (e.g., Veilleux and Cummings 2012), providing a more complete understanding of vision-mediated community dynamics however, an understanding of how ALAN might shift those dynamics from a mechanistic (i.e., individual) level is lacking. This is particularly important for estuaries and other coastal areas, which are experiencing human population growth at a rate three times greater than the global average (Small and Nicholls 2003), with concomitant increases in ALAN.

Missing the Dark: Health Effects of Light Pollution

In 1879, Thomas Edison’s incandescent light bulbs first illuminated a New York street, and the modern era of electric lighting began. Since then, the world has become awash in electric light. Powerful lamps light up streets, yards, parking lots, and billboards. Sports facilities blaze with light that is visible for tens of miles. Business and office building windows glow throughout the night. According to the Tucson, Arizona–based International Dark-Sky Association (IDA), the sky glow of Los Angeles is visible from an airplane 200 miles away. In most of the world’s large urban centers, stargazing is something that happens at a planetarium. Indeed, when a 1994 earthquake knocked out the power in Los Angeles, many anxious residents called local emergency centers to report seeing a strange “giant, silvery cloud” in the dark sky. What they were really seeing—for the first time—was the Milky Way, long obliterated by the urban sky glow.

None of this is to say that electric lights are inherently bad. Artificial light has benefited society by, for instance, extending the length of the productive day, offering more time not just for working but also for recreational activities that require light. But when artificial outdoor lighting becomes inefficient, annoying, and unnecessary, it is known as light pollution. Many environmentalists, naturalists, and medical researchers consider light pollution to be one of the fastest growing and most pervasive forms of environmental pollution. And a growing body of scientific research suggests that light pollution can have lasting adverse effects on both human and wildlife health.

When does nuisance light become a health hazard? Richard Stevens, a professor and cancer epidemiologist at the University of Connecticut Health Center in Farmington, Connecticut, says light photons must hit the retina for biologic effects to occur. “However, in an environment where there is much artificial light at night—such as Manhattan or Las Vegas—there is much more opportunity for exposure of the retina to photons that might disrupt circadian rhythm,” he says. “So I think it is not only ‘night owls’ who get those photons. Almost all of us awaken during the night for periods of time, and unless we have blackout shades there is some electric lighting coming in our windows. It is not clear how much is too much that is an important part of the research now.”

According to “The First World Atlas of the Artificial Night Sky Brightness,” a report on global light pollution published in volume 328, issue 3 (2001) of the Monthly Notices of the Royal Astronomical Society, two-thirds of the U.S. population and more than one-half of the European population have already lost the ability to see the Milky Way with the naked eye. Moreover, 63% of the world population and 99% of the population of the European Union and the United States (excluding Alaska and Hawaii) live in areas where the night sky is brighter than the threshold for light-polluted status set by the International Astronomical Union—that is, the artificial sky brightness is greater than 10% of the natural sky brightness above 45° of elevation.

Light pollution comes in many forms, including sky glow, light trespass, glare, and over illumination. Sky glow is the bright halo that appears over urban areas at night, a product of light being scattered by water droplets or particles in the air. Light trespass occurs when unwanted artificial light from, for instance, a floodlight or streetlight spills onto an adjacent property, lighting an area that would otherwise be dark. Glare is created by light that shines horizontally. Overillumination refers to the use of artificial light well beyond what is required for a specific activity, such as keeping the lights on all night in an empty office building.

Distracted by the Light

The ecologic effects of artificial light have been well documented. Light pollution has been shown to affect both flora and fauna. For instance, prolonged exposure to artificial light prevents many trees from adjusting to seasonal variations, according to Winslow Briggs’s chapter on plant responses in the 2006 book Ecological Consequences of Artificial Night Lighting. This, in turn, has implications for the wildlife that depend on trees for their natural habitat. Research on insects, turtles, birds, fish, reptiles, and other wildlife species shows that light pollution can alter behaviors, foraging areas, and breeding cycles, and not just in urban centers but in rural areas as well.

Sea turtles provide one dramatic example of how artificial light on beaches can disrupt behavior. Many species of sea turtles lay their eggs on beaches, with females returning for decades to the beaches where they were born to nest. When these beaches are brightly lit at night, females may be discouraged from nesting in them they can also be disoriented by lights and wander onto nearby roadways, where they risk being struck by vehicles.

Moreover, sea turtle hatchlings normally navigate toward the sea by orienting away from the elevated, dark silhouette of the landward horizon, according to a study published by Michael Salmon of Florida Atlantic University and colleagues in volume 122, number 1–2 (1992) of Behaviour. When there are artificial bright lights on the beach, newly hatched turtles become disoriented and navigate toward the artificial light source, never finding the sea.

Jean Higgins, an environmental specialist with the Florida Wildlife Conservation Commission Imperiled Species Management Section, says disorientation also contributes to dehydration and exhaustion in hatchlings. “It’s hard to say if the ones that have made it into the water aren’t more susceptible to predation at this later point,” she says.

Bright electric lights can also disrupt the behavior of birds. About 200 species of birds fly their migration patterns at night over North America, and especially during inclement weather with low cloud cover, they routinely are confused during passage by brightly lit buildings, communication towers, and other structures. “Light attracts birds and disorients them,” explains Michael Mesure, executive director of the Toronto-based Fatal Light Awareness Program (FLAP), which works to safeguard migratory birds in the urban environment. “It is a serious situation because many species that collide frequently are known to be in long-term decline and some are already designated officially as threatened.”

Each year in New York City alone, about 10,000 migratory birds are injured or killed crashing into skyscrapers and high-rise buildings, says Glenn Phillips, executive director of the New York City Audubon Society. The estimates as to the number of birds dying from collisions across North America annually range from 98 million to close to a billion. The U.S. Fish and Wildlife Service estimates 5–50 million birds die each year from collisions with communication towers.

Turtles and birds are not the only wildlife affected by artificial nighttime lighting. Frogs have been found to inhibit their mating calls when they are exposed to excessive light at night, reducing their reproductive capacity. The feeding behavior of bats also is altered by artificial light. Researchers have blamed light pollution for declines in populations of North American moths, according to Ecological Consequences of Artificial Night Lighting. Almost all small rodents and carnivores, 80% of marsupials, and 20% of primates are nocturnal. “We are just now understanding the nocturnality of many creatures,” says Chad Moore, Night Sky Program manager with the National Park Service. “Not protecting the night will destroy the habitat of many animals.”

Resetting the Circadian Clock

The health effects of light pollution have not been as well defined for humans as for wildlife, although a compelling amount of epidemiologic evidence points to a consistent association between exposure to indoor artificial nighttime light and health problems such as breast cancer, says George Brainard, a professor of neurology at Jefferson Medical College, Thomas Jefferson University in Philadelphia. “That association does not prove that artificial light causes the problem. On the other hand, controlled laboratory studies do show that exposure to light during the night can disrupt circadian and neuroendocrine physiology, thereby accelerating tumor growth.”

The 24-hour day/night cycle, known as the circadian clock, affects physiologic processes in almost all organisms. These processes include brain wave patterns, hormone production, cell regulation, and other biologic activities. Disruption of the circadian clock is linked to several medical disorders in humans, including depression, insomnia, cardiovascular disease, and cancer, says Paolo Sassone-Corsi, chairman of the Pharmacology Department at the University of California, Irvine, who has done extensive research on the circadian clock. “Studies show that the circadian cycle controls from ten to fifteen percent of our genes,” he explains. “So the disruption of the circadian cycle can cause a lot of health problems.”

On 14–15 September 2006 the National Institute of Environmental Health Sciences (NIEHS) sponsored a meeting that focused on how best to conduct research on possible connections between artificial lighting and human health. A report of that meeting in the September 2007 issue of EHP stated, “One of the defining characteristics of life in the modern world is the altered patterns of light and dark in the built environment made possible by use of electric power.” The meeting report authors noted it may not be entirely coincidental that dramatic increases in the risk of breast and prostate cancers, obesity, and early-onset diabetes have mirrored the dramatic changes in the amount and pattern of artificial light generated during the night and day in modern societies over recent decades. “The science underlying these hypotheses has a solid base,” they wrote, “and is currently moving forward rapidly.”

The connection between artificial light and sleep disorders is a fairly intuitive one. Difficulties with adjusting the circadian clock can lead to a number of sleep disorders, including shift-work sleep disorder, which affects people who rotate shifts or work at night, and delayed sleep–phase syndrome, in which people tend to fall asleep very late at night and have difficulty waking up in time for work, school, or social engagements.

The sleep pattern that was the norm before the invention of electric lights is no longer the norm in countries where artificial light extends the day. In the 2005 book At Day’s Close: Night in Times Past, historian Roger Ekirch of Virginia Polytechnic Institute described how before the Industrial Age people slept in two 4-hour shifts (“first sleep” and “second sleep”) separated by a late-night period of quiet wakefulness.

Thomas A. Wehr, a psychiatrist at the National Institute of Mental Health, has studied whether humans would revert back to the two-shift sleep pattern if they were not exposed to the longer photoperiod afforded by artificial lighting. In the June 1992 Journal of Sleep Research, Wehr reported his findings on eight healthy men, whose light/dark schedule was shifted from their customary 16 hours of light and 8 hours of dark to a schedule in which they were exposed to natural and electric light for 10 hours, then darkness for 14 hours to simulate natural durations of day and night in winter. The subjects did indeed revert to the two-shift pattern, sleeping in two sessions of about 4 hours each separated by 1–3 hours of quiet wakefulness.

Beyond Sleep Disorders

Alteration of the circadian clock can branch into other effects besides sleep disorders. A team of Vanderbilt University researchers considered the possibility that constant artificial light exposure in neonatal intensive care units could impair the developing circadian rhythm of premature babies. In a study published in the August 2006 issue of Pediatric Research, they exposed newborn mice (comparable in development to 13-week-old human fetuses) to constant artificial light for several weeks. The exposed mice were were unable to maintain a coherent circadian cycle at age 3 weeks (comparable to a full-term human neonate). Mice exposed for an additional 4 weeks were unable to establish a regular activity cycle. The researchers concluded that excessive artificial light exposure early in life might contribute to an increased risk of depression and other mood disorders in humans. Lead researcher Douglas McMahon notes, “All this is speculative at this time, but certainly the data would indicate that human infants benefit from the synchronizing effect of a normal light/dark cycle.”

Since 1995, studies in such journals as Epidemiology, Cancer Causes and Control, the Journal of the National Cancer Institute, and Aviation Space Environmental Medicine, among others, have examined female employees working a rotating night shift and found that an elevated breast cancer risk is associated with occupational exposure to artificial light at night. Mariana Figueiro, program director at the Lighting Research Center of Rensselaer Polytechnic Institute in Troy, New York, notes that permanent shift workers may be less likely to be disrupted by night work because their circadian rhythm can readjust to the night work as long as light/dark patterns are controlled.

In a study published in the 17 October 2001 Journal of the National Cancer Institute, Harvard University epidemiologist Eva S. Schernhammer and colleagues from Brigham and Women’s Hospital in Boston used data from the 1988 Nurses’ Health Study (NHS), which surveyed 121,701 registered female nurses on a range of health issues. Schernhammer and her colleagues found an association between breast cancer and shift work that was restricted to women who had worked 30 or more years on rotating night shifts (0.5% of the study population).

In another study of the NHS cohort, Schernhammer and colleagues also found elevated breast cancer risk associated with rotating night shift work. Discussing this finding in the January 2006 issue of Epidemiology, they wrote that shift work was associated with only a modest increased breast cancer risk among the women studied. The researchers further wrote, however, that their study’s findings “in combination with the results of earlier work, reduce the likelihood that this association is due solely to chance.”

Schernhammer and her colleagues have also used their NHS cohort to investigate the connection between artificial light, night work, and colorectal cancer. In the 4 June 2003 issue of the Journal of the National Cancer Institute, they reported that nurses who worked night shifts at least 3 times a month for 15 years or more had a 35% increased risk of colorectal cancer. This is the first significant evidence so far linking night work and colorectal cancer, so it’s too early to draw conclusions about a causal association. “There is even less evidence about colorectal cancer and the larger subject of light pollution,” explains Stevens. “That does not mean there is no effect, but rather, there is not enough evidence to render a verdict at this time.”

The research on the shift work/cancer relationship is not conclusive, but it was enough for the International Agency for Research on Cancer (IARC) to classify shift work as a probable human carcinogen in 2007. “The IARC didn’t definitely call night shift work a carcinogen,” Brainard says. “It’s still too soon to go there, but there is enough evidence to raise the flag. That’s why more research is still needed.”

The Role of Melatonin

Brainard and a growing number of researchers believe that melatonin may be the key to understanding the shift work/breast cancer risk association. Melatonin, a hormone produced by the pineal gland, is secreted at night and is known for helping to regulate the body’s biologic clock. Melatonin triggers a host of biologic activities, possibly including a nocturnal reduction in the body’s production of estrogen. The body produces melatonin at night, and melatonin levels drop precipitously in the presence of artificial or natural light. Numerous studies suggest that decreasing nocturnal melatonin production levels increases an individual’s risk of developing cancer. [For more information on melatonin, see “Benefits of Sunlight: A Bright Spot for Human Health,” EHP 116:A160–A167 (2008).]

One groundbreaking study published in the 1 December 2005 issue of Cancer Research implicated melatonin deficiency in what the report authors called a rational biologic explanation for the increased breast cancer risk in female night shift workers. The study involved female volunteers whose blood was collected under three different conditions: during daylight hours, during the night after 2 hours of complete darkness, and during the night after exposure to 90 minutes of artificial light. The blood was injected into human breast tumors that were transplanted into rats. The tumors infused with melatonin-deficient blood collected after exposure to light during the night were found to grow at the same speed as those infused with daytime blood. The blood collected after exposure to darkness slowed tumor growth.

“We now know that light suppresses melatonin, but we are not saying it is the only risk factor,” says first author David Blask, a research scientist at the Bassett Healthcare Research Institute in Cooperstown, New York. “But light is a risk factor that may explain [previously unexplainable phenomena]. So we need to seriously consider it.”

The National Cancer Institute estimates that 1 in 8 women will be diagnosed with breast cancer at some time during her life. We can attribute only about half of all breast cancer cases to known risk factors, says Brainard. Meanwhile, he says, the breast cancer rate keeps climbing—incidence increased by more than 40% between 1973 and 1998, according to the Breast Cancer Fund—and “we need to understand what’s going on as soon as possible.”

Linking Light Pollution to Human Health

The evidence that indoor artificial light at night influences human health is fairly strong, but how does this relate to light pollution? The work in this area has just begun, but two studies in Israel have yielded some intriguing findings. Stevens was part of a study team that used satellite photos to gauge the level of nighttime artificial light in 147 communities in Israel, then overlaid the photos with a map detailing the distribution of breast cancer cases. The results showed a statistically significant correlation between outdoor artificial light at night and breast cancer, even when controlling for population density, affluence, and air pollution. Women living in neighborhoods where it was bright enough to read a book outside at midnight had a 73% higher risk of developing breast cancer than those residing in areas with the least outdoor artificial lighting. However, lung cancer risk was not affected. The findings appeared in the January 2008 issue of Chronobiology International.

“It may turn out that artificial light exposure at night increases risk, but not entirely by the melatonin mechanism, so we need to do more studies of ‘clock’ genes—nine have so far been identified—and light exposure in rodent models and humans,” Stevens says. Clock genes carry the genetic instructions to produce protein products that control circadian rhythm. Research needs to be done not just on the light pollution–cancer connection but also on several other diseases that may be influenced by light and dark.

Travis Longcore, co-editor of Ecological Consequences of Artificial Night Lighting and a research associate professor at the University of Southern California Center for Sustainable Cities, suggests two ways outdoor light pollution may contribute to artificial light–associated health effects in humans. “From a human health perspective, it seems that we are concerned with whatever increases artificial light exposure indoors at night,” he says. “The effect of outdoor lighting on indoor exposure could be either direct or indirect. In the direct impact scenario, the artificial light from outside reaches people inside at night at levels that affect production of hormones. In an indirect impact it would disturb people inside, who then turn on lights and expose themselves to more light.”

“The public needs to know about the factors causing [light pollution], but research is not going at the pace it should,” Blask says. Susan Golden, distinguished professor at the Center for Research on Biological Clocks of Texas A&M University in College Station, Texas, agrees. She says, “Light pollution is still way down the list of important environmental issues needing study. That’s why it’s so hard to get funds to research the issue.”

“The policy implications of unnecessary light at night are enormous,” says Stevens in reference to the health and energy ramifications [for more on the energy impact of light pollution, see “Switch On the Night: Policies for Smarter Lighting,” p. A28 this issue]. “It is fully as important an issue as global warming.” Moreover, he says, artificial light is a ubiquitous environmental agent. “Almost everyone in modern society uses electric light to reduce the natural daily dark period by extending light into the evening or before sunrise in the morning,” he says. “On that basis, we are all exposed to electric light at night, whereas before electricity, and still in much of the developing world, people get twelve hours of dark whether they are asleep or not.”

Sources believe that the meeting at the NIEHS in September 2006 was a promising beginning for moving forward on the light pollution issue. “Ten years ago, scientists thought something was there, but couldn’t put a finger on it,” says Leslie Reinlib, a program director at the NIEHS who helped organize the meeting. “Now we are really just at the tip of the iceberg, but we do have something that’s scientific and can be measured.”

The 23 participants at the NIEHS-sponsored meeting identified a research agenda for further study that included the functioning of the circadian clock, epidemiologic studies to define the artificial light exposure/disease relationship, the role of melatonin in artificial light–induced disease, and development of interventions and treatments to reduce the impact of light pollution on disease. “It was a very significant meeting,” Brainard says. “It’s the first time the National Institutes of Health sponsored a broad multidisciplinary look at the light-environmental question with the intent of moving to the next step.”

Glare, overillumination, and sky glow (which makes the sky over a city look orange, yellow, or pink) are all forms of light pollution. These photos were taken in Goodwood, Ontario, a small town about 45 minutes northeast of Toronto during and the night after the regionwide 14 August 2003 blackout. The lights inside the house in the blackout picture were created by candles and flashlights.

How Outdoor Lighting Translates into Light Pollution

Turtle hatchlings instinctively orient away from the dark silhouette of the nighttime shore. Here hatchlings have been temporarily distracted by a bright lamp. Hatchlings and mother turtles distracted by shorefront lights can wander onto nearby roadways.

Increase in Artificial Night Sky Brightness in North America

The International Agency for Research on Cancer has classified shift work as a probable human carcinogen. A study in the December 2008 issue of Sleep found that use of light exposure therapy, sunglasses, and a strict sleep schedule may help night-shift workers achieve a better-balanced circadian rhythm.

From hormonal axes to function

To fully appreciate how different endocrine axes might mediate individual responses to ALAN, we must first understand how hormones can affect behavioral and physiological function. Hormonal systems are powerful physiological mechanisms by which organisms can flexibly adjust their behavior, morphology and physiology to varying environmental conditions (Zera et al., 2007). Therefore, they are one of the first mediators of the effects of ALAN, and the disruption of endocrine responses may also have pleiotropic effects on whole organism function (Table 1 Fig. 2). After light has been perceived by the organism, hormones act as part of an effector system that will transmit information on light to the rest of the body. In this section, we will review the effects of ALAN on four endocrine axes, and how organismal fitness is affected by changes in their function.

Different endocrine axes affected by artificial light at night that lead to changes in potential fitness components. Solid lines indicate direct causal pathways and dashed lines indicate indirect pathways. GnIH, gonadotrophin-inhibitory hormone GnRH, gonadotrophin-releasing hormone HPA, hypothalamic–pituitary–adrenal HPG, hypothalamic–pituitary–gonadal HPT, hypothalamic–pituitary–thyroid.

Different endocrine axes affected by artificial light at night that lead to changes in potential fitness components. Solid lines indicate direct causal pathways and dashed lines indicate indirect pathways. GnIH, gonadotrophin-inhibitory hormone GnRH, gonadotrophin-releasing hormone HPA, hypothalamic–pituitary–adrenal HPG, hypothalamic–pituitary–gonadal HPT, hypothalamic–pituitary–thyroid.

Pineal axis

The pineal gland plays a crucial role in the regulation of daily and seasonal rhythms of vertebrates. This organ is found in all vertebrate classes, from fishes (Falcón et al., 2003) to amphibians (Dodt and Heerd, 1962), reptiles (Underwood, 1977), birds (Cassone, 2014) and mammals (Arendt and Skene, 2005). The most important function of the pineal gland is to produce and release the hormone melatonin, which conveys information about light–dark cycles and day length, thereby maintaining temporal organization of physiology and behavior. Importantly, in many species such rhythms are endogenously produced, and persist when the animal is placed in constant environmental conditions, such as constant darkness or constant light (Daan and Aschoff, 1975). Changes in the light environment synchronize, or ‘entrain’, such endogenous rhythms to the optimal time of day, night or even season, when they are supposed to be expressed. Although the pineal gland and the function of melatonin have been extensively studied in birds and mammals, here we attempt to broaden the field of reference to other vertebrate groups wherever possible. In this section, we focus on the effects of ALAN only on pineal functions that modify daily rhythms. We will consider seasonal rhythms in the next section, which will concern reproduction, as these are not always mediated by melatonin.

Daily timing and light at night

The pineal gland exhibits strong endogenous regulation of its rhythm of melatonin synthesis and secretion in lower vertebrates, whereas in mammals the pineal rhythm is driven by a neural input. For instance, in birds it is possible to culture pineal cells in vitro without the cells losing their endogenous circadian release of melatonin (Arendt, 1998 Brandstätter et al., 2000 Gaston and Menaker, 1968 Robertson and Takahashi, 1988). Experiments both in vivo (in plasma samples) and in vitro (cultured pineal cells) have demonstrated that rhythms of melatonin are comparable (Brandstätter et al., 2001). This is not possible for the mammalian pineal gland as pinealectomy does not lead to disrupted circadian rhythms unless the animal is kept in constant bright light (Valdés-Tovar et al., 2015 Vinogradova et al., 2010), when animals present signs of splitting, fragmentation or damping of activity rhythms (Cassone, 1990).

The daily timing of melatonin secretion is highly conserved across all vertebrates (Reiter et al., 2014). Melatonin is secreted by the pineal gland during the night and is suppressed by light during the daytime. In mammals, the secretion of melatonin is largely controlled by the SCN, which then regulates pineal rhythms via neural inputs. In birds, the pineal gland possesses its own set of photoreceptors (Peirson et al., 2009), and is therefore able to produce melatonin independently of the SCN (Bell-Pedersen et al., 2005). However, in non-mammalian vertebrates it is also clear that melatonin is not an exclusive product of the pineal gland, but it can be synthesized by other organs and tissue. For instance, in birds, amphibians and fishes, the eyes are also capable of melatonin production (Underwood et al., 1984).

The duration of melatonin release varies between species, but it is generally assumed to reflect the length of the night and thereby the photoperiod (Arendt, 1998 Gwinner et al., 1997). Light pulses of different duration and intensity, delivered at night, can suppress melatonin levels in humans and other vertebrates (Arendt, 1998 Wikelski et al., 2008). Therefore, ALAN has been suggested to alter the perception of day length and influence the regulation of daily and seasonal rhythms (Dominoni, 2015 Dominoni and Partecke, 2015). Indeed, exposure to ALAN has been associated with changes in diel (see Glossary) activity patterns in several species across all vertebrate taxa (Bird et al., 2004 de Jong et al., 2016 Dominoni et al., 2014 Kempenaers et al., 2010 Migaud et al., 2007 Ouyang et al., 2017b Perry et al., 2008 Raap et al., 2015 Rotics et al., 2011). In humans, partial suppression of melatonin can be achieved by exposure to 100–300 lx for 2 h, although for complete suppression, an intensity of 2500 lx is required (Fig. 1) (Arendt, 1998 Dauchy et al., 2014 Stevens and Zhu, 2015). In captive birds, it has long been known that light pulses during the night can reduce melatonin concentrations (Gwinner et al., 1997 Vakkuri et al., 1985). Two recent studies in captivity have tested the hypothesis that nocturnal light of an intensity comparable to that found in urban environments can suppress melatonin rhythms. The first study showed that whole-night exposure to a light intensity of 0.3 lx is able to suppress melatonin concentrations to baseline values in the European blackbird (Turdus merula), especially in the early morning, with milder effects in the early and mid-night (Fig. 3 Dominoni et al., 2013b). The second study, on great tits (Parus major), revealed that increasing levels of light intensity given over the whole night are linearly associated with a decrease in plasma melatonin levels (de Jong et al., 2016). Similar results have been found in fishes, where exposure to as little as 2 lx of light for 1 h in the middle of the night is able to decrease melatonin levels in serum, and this decrease is linearly related to light intensity (Bayarri et al., 2002 Zachmann et al., 1992). However, in reptiles, which are phylogenetically closer to birds, light pulses during the night are, surprisingly, unable to reduce melatonin levels. This negative result has been found in both lizards and turtles (Underwood, 1986 Vivien-Roels et al., 1988), and the investigators suggest that, in these species, light might affect pineal-originated melatonin indirectly via its synchronizing effect of circadian oscillators, rather than directly via changes in the activity of N-acetyltransferase, the enzyme that initiates melatonin production in birds and mammals. Importantly, the degree of melatonin suppression by ALAN not only depends on the light intensity, but also on the light spectrum. Indeed, in humans, short wavelengths corresponding to blue light have been shown to elicit a much stronger suppressive effect on melatonin levels than longer wavelengths, such as orange-red light (Aubé et al., 2013 Cajochen et al., 2005 Navara and Nelson, 2007). This wavelength-dependent effect of light on melatonin suppression is used by some computer monitors and electronic devices, which can shift the spectrum of light emitted toward more orange and less blue light during the night time. Similar wavelength-dependent effects have also been found in rodents (Nelson and Takahashi, 1991 Zubidat et al., 2011), birds (Lewis et al., 2001 Surbhi and Kumar, 2015) and fishes (Oliveira et al., 2007 Vera et al., 2010 Ziv et al., 2007). Therefore, it is generally accepted that short to mid wavelengths can suppress melatonin levels, and thus affect circadian physiology to a greater extent than longer wavelengths.

Effects of exposure to ALAN on daily and seasonal concentration of melatonin and testosterone in male urban and forest European blackbirds (Turdus merula). Melatonin (A) and testosterone (B) levels in plasma from an equal number of forest and urban birds exposed to two different treatments: either dark nights (control) or artificial light at night (experimental). Experimental birds were exposed to a constant intensity of artificial light level throughout the night, equal to 0.3 lx, and produced by an incandescent light bulb with a wavelength range between 450 and 950 nm. Control birds were exposed to dark nights. Photoperiod followed the natural variation in daylength in Radolfzell, Germany and was changed on a daily basis. Daytime light intensity was ∼600 lx and was provided by fluorescent white bulbs. Both hormones were analysed on plasma samples obtained from the same individuals at different times. Blood sampling for melatonin was conducted in winter (Jan 25 to 29, 2011). Blood sampling for testosterone was conducted approximately every 3 weeks during the period of Dec 2010 to Aug 2011. Figures adapted from Dominoni et al. (2013a,b).

Effects of exposure to ALAN on daily and seasonal concentration of melatonin and testosterone in male urban and forest European blackbirds (Turdus merula). Melatonin (A) and testosterone (B) levels in plasma from an equal number of forest and urban birds exposed to two different treatments: either dark nights (control) or artificial light at night (experimental). Experimental birds were exposed to a constant intensity of artificial light level throughout the night, equal to 0.3 lx, and produced by an incandescent light bulb with a wavelength range between 450 and 950 nm. Control birds were exposed to dark nights. Photoperiod followed the natural variation in daylength in Radolfzell, Germany and was changed on a daily basis. Daytime light intensity was ∼600 lx and was provided by fluorescent white bulbs. Both hormones were analysed on plasma samples obtained from the same individuals at different times. Blood sampling for melatonin was conducted in winter (Jan 25 to 29, 2011). Blood sampling for testosterone was conducted approximately every 3 weeks during the period of Dec 2010 to Aug 2011. Figures adapted from Dominoni et al. (2013a,b).

Circadian homeostasis is essential for the maintenance of body function and health. When circadian rhythms are disrupted, for instance through sleep deprivation or shift work, negative health consequences can appear. This has been demonstrated in cross-sectional human studies as well as in more rigorous experiments in model species (Buxton et al., 2012 McFadden et al., 2014 Möller-Levet et al., 2013 Navara and Nelson, 2007 Stevens, 2009). Since ALAN is a potent agent of modification of circadian rhythms, it has been implicated in the emergence of several human diseases, from metabolic syndrome and obesity (Fonken et al., 2010 Navara and Nelson, 2007), to depression (Bedrosian et al., 2013 Stevens and Zhu, 2015) and cancer (Stevens, 2009). However, this aspect is much less studied in wild animals (Dominoni et al., 2016). Recent work has suggested that wild species, and in particular birds, might be sleep deprived when exposed to ALAN, although with only mild physiological health consequences (Ouyang et al., 2017b Raap et al., 2016, 2015). Whether such effects can impair fitness remains to be established.

Reproductive axis

The relationship between light, circadian rhythms and the perception of day length profoundly affects seasonal processes, and forms the basis for understanding the potential effects of ALAN on seasonal rhythms and reproduction. Central to photoperiodism is the role of the hypothalamic–pituitary–gonadal (HPG) axis (see Glossary) (Dawson, 2015), a well conserved system across vertebrates (Sower et al., 2009). HPG axis activity begins with secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus into the hypophyseal portal blood vessels. GnRH stimulates the anterior pituitary to secrete gonadotropins [luteinizing hormone (LH) and follicle stimulating hormone (FSH)], which elicit gonadal maturation and secretion of sex steroids (estrogens and androgens). The neural pathway that detects day length and transduces this information to the HPG axis varies between vertebrate classes (Ikegami and Yoshimura, 2016). In mammals, light is detected through the eyes, and the signals are transduced to the pineal gland, which then releases melatonin (as detailed above). In addition, recent work has elucidated the molecular mechanism behind the action of melatonin on mammalian seasonal reproduction (Hut, 2011). A specific area in the pituitary, the pars tuberalis (PT), is packed with melatonin receptors. Under long photoperiods (usually more than 14 h of light per day), a physiological cascade is initiated in the PT that stimulates the production of thyroid hormones in the adjacent basal hypothalamus, ultimately influencing the secretion of GnRH. A similar mechanism has been recently uncovered in birds (Nakao et al., 2008).

Studies on birds have also been instrumental in the understanding of the relationship between light, circadian rhythms and seasonal processes. Indeed, it has long been known that single, short light pulses in the middle of the night are able to trigger reproductive responses (gonadal growth, LH secretion) even when the animal is kept under short, non-stimulatory day lengths (Follett et al., 1974 Te Marvelde et al., 2012). These studies suggest the existence of a circadian rhythm in photosensitivity that mediates seasonal reproduction in birds. Importantly, the photoreceptors involved in such responses are located in the avian hypothalamus (Davies et al., 2012 Halford et al., 2009 Nakane et al., 2010). Thus, it is reasonable to hypothesize that even brief pulses of ALAN might directly affect reproductive timing via stimulation of deep brain photoreceptors. A competing or complementary hypothesis is that ALAN does not directly stimulate the photoreceptors, but instead indirectly affects seasonal reproduction by influencing other processes, such as foraging and social interactions. As discussed below, future research is necessary to establish which hypothesis is correct.

Seasonally breeding vertebrates that use photoperiod as the main reproductive cue can be broadly categorized into either long- or short-day breeders, depending on the day length when they are fertile. Long-day breeders (e.g. horses, hamsters, birds and most non-avian reptiles) are fertile during spring when day length is increasing, whereas short-day breeders (e.g. sheep, goats, foxes and deer) are fertile during autumn when day length is decreasing. A growing number of studies have found that the timing of seasonal reproductive processes differs between vertebrates inhabiting areas with ALAN and their conspecifics inhabiting areas with little or no ALAN (Brüning et al., 2015 de Jong et al., 2015 Dominoni et al., 2013a Ikeno et al., 2014 LeTallec et al., 2015 Schoech et al., 2013). Given the central role of day length in regulating seasonal reproduction, one hypothesis to explain these findings is that ALAN stimulates the photoreceptors that activate the HPG axis, thereby altering the perceived day length and modifying the timing of reproductive processes (Fig. 3). Following this hypothesis, ALAN should advance the increase in day length that long-day breeders use to initiate HPG axis activity. In turn, long-day breeders should advance the timing of reproductive maturation and breeding. By contrast, ALAN should delay or even completely inhibit the decrease in day length that short-day breeders use to time reproductive maturation and breeding. The available evidence from studies of free-ranging vertebrates is consistent with these predictions. Studies of long-day breeders have focused mainly on birds, and have generally found that birds living in areas with ALAN initiate seasonal reproductive processes earlier than birds in areas lacking ALAN (de Molenaar et al., 2006 Kempenaers et al., 2010 Russ et al., 2015). Among short-day breeders, Robert et al. (2015) found that female tammar wallabies (Macropus eugenii) living in areas with ALAN gave birth later than wallabies living in areas free of ALAN. The authors suggest that it is because ALAN masks the small decreases in day length following the summer solstice that wallabies use to time the reactivation of blastocysts. In European perch (Perca fluvialis), another short-day breeder, ALAN completely inhibits gonadotropins (LH and FSH) production. However, it is important to note that although the effects of ALAN on the reproductive physiology are generally strong and well established, this does not necessarily mean that the actual breeding time will be affected. For instance, although ALAN can stimulate gonadal growth in birds up to 1 month earlier than usual, this translates into egg-laying only a few days earlier than usual, and even this is not observed every year (de Jong et al., 2015 Kempenaers et al., 2010). This is likely because egg-laying date is mediated by supplementary cues other than photoperiod, such as temperature and availability of food (Schaper et al., 2012 Te Marvelde et al., 2012).

Although the studies in controlled conditions generally find that ALAN affects the timing of seasonal reproductive processes, they do not demonstrate that ALAN exerts its effects by directly stimulating the non-image-forming photoreceptors. As such, it still cannot be excluded that ALAN indirectly affects seasonal reproduction by influencing other processes, including foraging and social interactions. ALAN-induced increases in perceived day length potentially give vertebrates more time each day to forage and for social interactions. More time to forage could potentially improve the likelihood that animals have sufficient energy stores for breeding, which is thought to be particularly important for females (Davies and Deviche, 2014). Furthermore, ALAN has been shown to improve foraging efficiency of wading birds (Regular et al., 2011 Santos et al., 2010). Increases in apparent day length as a result of ALAN may also provide time for more social interactions between males and females. It is well known that the onset of dawn song is earlier in birds inhabiting areas with ALAN (Kempenaers et al., 2010 Miller, 2006). Changes in the timing of reproductive processes could, therefore, be related to ALAN-induced changes in the behavior of the opposite sex. Indeed, it is well established that social interactions between males and females can modulate reproductive processes. For example, male song has rapid endocrine and behavioral effects on females (Maney et al., 2007, 2003) and can stimulate ovarian development (Bentley et al., 2000). Likewise, males can respond to estradiol-treated females by elevating their plasma testosterone (Wingfield and Monk, 1994).

A major limitation of studies in the wild is that it is difficult to separate the effects of ALAN from the effects of other environmental variables that often accompany ALAN. Most studies of ALAN compare vertebrates in urban areas against vertebrates in non-artificially illuminated rural areas (for an exception, see de Jong et al., 2015). In addition to increased ALAN, urban areas also tend to be warmer (the so-called ‘urban heat island’ effect), noisier, have higher human density, altered plant phenology and possibly also altered food availability (Buyantuyev and Wu, 2012 Deviche and Davies, 2013 Halfwerk and Slabbekoorn, 2013 Imhoff et al., 2010). Accordingly, urban populations of long-day breeders generally begin reproductive processes earlier than their rural conspecifics (Deviche and Davies, 2013 Partecke et al., 2005). Studies in controlled conditions aiming to test whether ALAN by itself is sufficient to modify the timing of seasonal reproductive processes generally support the hypothesis that ALAN alters reproductive physiology consistent with the predictions above (Brüning et al., 2015 Dominoni et al., 2013a Ikeno et al., 2014 LeTallec et al., 2015 Schoech et al., 2013), and likely more strongly than other urban-specific factors, such as higher temperature and breeding density (Dominoni et al., 2015). Indeed, the effects of ALAN have been demonstrated at all levels of the HPG axis. However, these effects of ALAN are complex and can depend on which aspects of the HPG axis are considered and sex. This point is illustrated by the study of Schoech et al. (2013), which found differences in the responses of plasma LH, testosterone and estradiol to ALAN in male and female Western scrub jays (Aphelocoma californica). The cause of this variation between hormones and sexes remains to be determined.

Adrenal axis

The hypothalamic–pituitary–adrenal (HPA see Glossary) axis is responsible for responding to external stressors or challenges in the environment (Romero et al., 2009). Glucocorticoid hormones (GCs cortisol, corticosterone), released by the adrenals (see Glossary), are of particular importance for vertebrates as they serve diverse functions to maintain organismal energy balance (Hau and Goymann, 2015). GCs coordinate organismal response to predictable changes but also to acute, unpredictable challenges. Thus, they are mediators of individual phenotypic flexibility to changing environmental conditions (Hau et al., 2016).

An early study in rats found an elevation of corticosterone levels with constant exposure to fluorescent lighting (Scheving and Pauly, 1966). Interestingly, not only did the rats have elevated corticosterone levels, their diurnal rhythm of release was also disrupted. A series of laboratory studies in hamsters have shown that chronic light exposure decreases immune function and elevates cortisol levels (Bedrosian et al., 2011, 2013). In a laboratory study on fish, only salmon exposed to high-intensity blue LED light had increased cortisol levels whereas white LEDs and metal halide lights did not raise cortisol levels (Migaud et al., 2007). Free-living great tits breeding in white light at night had much higher GC levels than birds breeding in green, red or dark control sites (Ouyang et al., 2015). Differences in these two studies on the effects of LEDs can be attributed to study design or taxa-related ALAN perception and response. These elevated levels are typical for circulating levels seen after a restraint-and-capture stress series. This study was the first to look at GC levels in a free-living species and there were no differences in survival, which suggests that long-term fitness effects in the wild could be balanced by other factors, such as increases of food availability in white light (Welbers et al., 2017). These studies illustrate the importance of investigating GC levels in other taxa and under different lighting conditions as not all species seem to react to ALAN with an elevation of the HPA axis.

As widespread artificial light is a relatively recent phenomenon, upstream effects on receptors and receptor densities in the HPA axis have not been studied. In order to understand the full impact of ALAN on the HPA axis, we should be testing HPA reactivity (how high GC levels originate), as well as negative feedback (how increasingly high levels of GCs may inhibit further secretion). It could be that ALAN only affects negative feedback and/or receptor levels, which causes the downstream effects of elevated GCs. But only by probing the whole axis will we be able to counteract the effects of ALAN.

Thyroid axis

Thyroid hormones show pronounced daily and/or seasonal rhythms, and have been shown to strongly respond to changes in photoperiod. Thus, ALAN can potentially affect the secretion of these molecules, and thereby many physiological processes. Here, we briefly review the role of thyroid hormones (THs) in daily and seasonal biology, and then describe potential consequences of exposure to ALAN on thyroid function.

The daily and seasonal regulation of THs is well understood in vertebrates. THs are important regulators of energy homeostasis, and thyroid hormone receptors (THRs) are present in virtually all tissues (Williams and Bassett, 2011). T4 is the first TH that is produced and released in significant concentrations in the blood. T4 is converted into its active form, T3, through the action of the enzyme type II iodothyronine deiodinase (DIO2) in target tissues (Williams and Bassett, 2011). T3 is involved in several physiological processes, including growth and development, metabolism, regulation of body temperature and heart rate, and can be considered the main thyroid hormone (Eales, 1988 Mullur et al., 2014 Williams and Bassett, 2011). Photoperiod synchronizes the production of THs. For instance, in fishes, diurnal rhythms of circulating THs appear to be synchronized to the light cycle rather than to time of feeding (Leiner and MacKenzie, 2001 Reddy and Leatherland, 2003). Importantly, such rhythms persist in constant conditions for several cycles, suggesting the involvement of a light-sensitive endogenous circadian clock that determines the activation or inhibition of the hypothalamus–pituitary–thyroid (HPT) axis (Leiner and MacKenzie, 2001). Similar findings have been found across all vertebrates, from anurans (Gancedo et al., 1997) to birds (Cogburn and Freeman, 1987) and mammals (Eales, 1988). The time of day at which levels of T3 and T4 peak appears to differ across seasons (Gancedo et al., 1996 Yoshimura, 2010), underlying the role of seasonal changes in photoperiod in regulating thyroid function. Indeed, THs are a key component of the photoperiodic response across all vertebrates (Hazlerigg and Loudon, 2008 Hut, 2011).

So how could ALAN affect thyroid function? The most obvious way is through indirect effects due to changes in melatonin levels. As we outlined above, ALAN changes day length perception, and more specifically it is interpreted as a long day. Thereby, exposure to ALAN fundamentally shifts the entire physiology to longer-day-length-like conditions. As for thyroid action, increased day lengths initiate a physiological cascade that promotes the conversion of T4 into T3 and ultimately gonadal activation. Indeed, long photoperiods have been associated with increased levels of TSH and T3 in several species (Boeuf and Le Bail, 1999 Nakao et al., 2008 Yoshimura, 2010). Realistic levels of ALAN (5 lx) have been shown to increase the expression of TSH receptors in the hypothalamus and pars tuberalis of Siberian hamsters kept under short photoperiods, and this was accompanied by important physiological changes such as increased gonadal and body mass, suggesting that dim light at night can alter the molecular and physiological mechanisms underlying photoperiodic response, including thyroid function (Ikeno et al., 2014). However, chronic exposure to ALAN might have the opposite effect and reduce thyroid hormones to very low levels, as seen for testosterone in birds (Dominoni et al., 2013c). Indeed, studies on humans living in polar regions have highlighted the risk of the so-called ‘polar T3 syndrome’, a hallmark of which is chronically low levels of blood T3. Such syndromes are usually associated with psychological disorders such as depression and increased aggression, similar to seasonal affective disorders (SADs) (Palinkas and Suedfeld, 2008). Changes in thyroid hormone concentrations due to ALAN could also have indirect effects on a plethora of other physiological processes that are heavily regulated by thyroid action. In particular, energy metabolism is a key process that is under the influence of the thyroid (Mullur et al., 2014). A recent study has linked ALAN with reduced energy expenditure in wild birds (Welbers et al., 2017), but it is unclear whether thyroid hormones were at all involved in such metabolic changes. Overall, it is sensible to hypothesize several physiological consequences of light at night that could be mediated by changes in thyroid hormones. However, there is little empirical evidence for this so far, and some data point more to an indirect effect of ALAN on thyroid action via changes in circadian physiology and melatonin (Ikeno et al., 2014).

Scien tific studies on the negative effects of flicker from LED and Fluorescent lighting

Its important to look beyond just the high blue light output in our modern lighting, as there are other aspects of it such as flicker which is causing harm to our health. The studies below look at what flicker is and what impacts it is having on our health.

We have also written articles on the issues with modern lighting and cover the topic of flicker. You can read them here:
- The Horrors Of Working And Living Under Fluorescent & LED lights and LED
- Fluorescent Light Health Concerns: The Plot Thickens

"It is seen that with LED sources the severity and range of flicker is relatively very high when compared to conventional lights."

"The various adverse effects of flicker include eye strain, fatigue, headache, migraine, blurred vision as well as photo epilepsy in sensitive individuals"

"The purpose of the study was to compare the impact on subjective well-being, performance and physiological arousal of fluorescent light powered by conventional and high-frequency ballasts."

"Flickering light has been shown to have detrimental effects in humans and other species."


Light pollution is a rapidly growing threat to terrestrial and aquatic biodiversity worldwide ( Gaston et al., 2013 Koen et al., 2018). A growing body of research has elaborated the ways in which unnatural light at night impacts organisms and ecosystems, which include disruptions of sensory perception, diel cycle and ecological interactions ( Hölker et al., 2010 Davies et al., 2016). Such disruptions are underpinned by physiological processes, the study of which can inform how organisms respond to light pollution, particularly when its effects are not visible to the naked eye ( Navara and Nelson, 2007 Gaston et al., 2013). Most research on the subject has focused on terrestrial systems however, light pollution threatens marine and freshwater organisms and is less well understood in these aquatic environments ( Davies et al., 2016). Davies et al. (2014) estimated that 22% of coastal areas on Earth (excluding Antarctica) experience some degree of light pollution, which Kyba et al. (2017b) estimated is growing by 2.2% in area and brightness annually as coastal areas worldwide continue to rapidly urbanize ( Neumann et al., 2015).

Diverse biomarkers are used to assess how animals respond to extrinsic stimuli, including those of anthropogenic origin such as light pollution, which collectively contribute to allostatic load ( McEwen and Wingfield, 2010). In the context of wild organisms, there is particular interest in understanding how anthropogenic disturbances influence performance, fitness and population-level ecological processes ( Wikelski and Cooke, 2006, Dantzer et al., 2014). Light pollution has been found to disrupt hormone cycles or induce stress in several species of fish (inferred largely from glucocorticoids), such as European perch (Perca fluviatilis) ( Brüning et al., 2015, Brüning et al., 2018), bonefish (Albula vulpes) ( Szekeres et al., 2017), Atlantic salmon (Salmo salar) ( Migaud et al., 2007) and baunco (Girella laevifrons) ( Pulgar et al., 2019), along with altering aquatic animal behaviour ( Gaston et al., 2015 Thums et al., 2016 Fischer et al., 2020) and ecosystem structure ( Perkin et al., 2011 Underwood et al., 2017). Few studies have investigated the effect of light pollution on aquatic invertebrates, despite their abundance and integral significance in aquatic ecosystems. Moderate levels of artificial light at night (i.e. 4–15 lux) have been found to suppress activity and alter behaviour in four species of North American crayfish ( Jackson and Moore, 2019 Fischer et al., 2020), and the Japanese spiny lobster (Panulirus japonicus) has been reported to suppress activity at extremely low levels of artificial light at night (1.8 × 10 −4 lux) ( Nagata and Koike, 1997). We are aware of only one study to date that has measured hormones in an aquatic invertebrate subjected to artificial light at night in an attempt to understand if it contributed to allostatic load ( Jackson and Moore, 2019), which found that it did not affect levels of haemolymph serotonin in two species of North American crayfish, despite disrupting their behaviour and activity levels. While hormone levels can reflect an animal’s status over a given period of time prior to sampling, other endpoints can be used to assess stress responses more continuously and at higher resolution, such as heart rate (fH) and locomotor activity. Moreover, so-called ‘stress hormones’ (i.e. glucocorticoids) are increasingly recognized as having diverse roles in organism function ( MacDougall-Shackleton et al., 2019).

Heart rate has been used as a measure of physiological status and allostatic load in a range of animal taxa, including the decapod crustaceans. Decapods have the most complex circulatory system among crustaceans, similar to that of basal vertebrates, and changes in fH have been found to be a reliable indicator of physiological state in numerous decapod species ( McGaw and Reiber, 2015). As in fish and other vertebrates, fH often increases with exposure to stress however, decapods may also undergo bradycardia (slowing of fH) or acardia (temporary cessation of fH) when exposed to a physiological challenge depending on its rapidity, duration and severity ( Brown et al., 2004 McLean and Todgham, 2015). The measurement of fH in decapods has historically been confined to tethered or constrained animals however, McGaw et al. (2018) developed a novel methodology for measuring fH in free-moving decapods using fH biologgers. In addition, advances in acceleration biologger technology (i.e. accelerometers) have made it possible to remotely measure activity in small, free-moving animals ( Brown et al., 2013 Cooke et al., 2016), activity being a primary determinant of fH in decapods as well as a measure of behavioural response to a stimulus ( Bertelsen, 2013 Goldstein et al., 2015 Gutzler et al., 2015 Jury et al., 2018).

In this study, we used heart rate biologgers along with tri-axial accelerometers to explore the physiological and behavioural response of Caribbean spiny lobster (Panulirus argus) to light pollution. Panulirus argus forms one of the most culturally and economically significant fisheries in the western Atlantic Ocean, employing over 60 000 people and generating more than $1 billion in revenue annually ( Winterbottom et al., 2012 FAO, 2018 CLME+, 2019). In The Bahamas, where P. argus is known as crawfish, the fishery is the largest and most valuable in the country ( Smith and Zeller, 2013 Sherman et al., 2018) and the Bahamian fishery is the largest in the species’ range ( CLME+, 2019). While the Bahamian fishery was certified by the Marine Stewardship Council in 2018 ( Gascoigne et al., 2018), P. argus has had a ‘data deficient’ IUCN Red List status over its entire range since its last assessment in 2009 ( Butler et al., 2013) and its fisheries are likely overfished in many places ( CRFM, 2011 Winterbottom et al., 2012 WECAFC, 2018 CLME+, 2019). Panulirus argus is also an ecologically significant species, influencing community structure through predation, underpinning trophic linkages from chemosynthetic primary production and forming an important part of its predators’ diets ( Smith and Herrkind, 1992 Higgs et al., 2016 Gnanalingam and Butler IV, 2018). As a nocturnal generalist with a light-mediated circadian cycle of activity that forages in shallow nearshore areas, P. argus may be increasingly subjected to light pollution as coastal and offshore development near their habitat continues, and its heavily-exploited status may make this species particularly sensitive to emerging anthropogenic disturbances. To our knowledge, the effect of light pollution on any aspect of this species’ biology or ecology has not been investigated to date. As it has the potential to disrupt diel endocrine cycles that mediate physiological processes ( Castanon-Cervantes et al., 1999 McGaw and Reiber, 2015 Jackson and Moore, 2019), we hypothesized that artificial light at night would (1) increase fH in P. argus, indicating that it is contributing to allostatic load, and (2) decrease its nocturnal activity as has been found in P. japonicus and other decapods, indicating a behavioural alteration ( Nagata and Koike, 1997 Jackson and Moore, 2019 Fischer et al., 2020).


Pollution has been defined by Odum (1971) as “the undesirable change in the physical, chemical or biological characteristics of air, land and water that may affect the human life. The pollutants cause undesirable physical and biological changes.

Man is searching for food and better living conditions. It has destroyed the environment. Man has added a lot of dust, smoke, poisonous gases and radiations in the atmosphere. He has created problem of soil erosion, waterlogging and salinity. He has added injurious chemicals to the soil, river and sea due to the pesticide and fertilizers. He is throwing poisonous liquid, solid and gaseous waste in the surroundings. He has developed weapons and produced dangerous chemicals to kill other humans. Thus he is increasing pollution in the environment.

Odum defines pollutant as “residues of things we make, use and thraw away are called pollutants. The pollutants may be:

  1. The pollutant may be gases like CO, SO2 etc.
  1. These may be metals like lead, zinc, chromium etc.
  2. There may be industrial pollutants like cyanide compounds, acetic acid acids.
  3. Agriculture pollutants are pesticides, herbicides, fungicides and fertilizers.
  4. Photochemical pollutants are ozone oxides, CFC (Chloroflouro carbon).
  5. Radiations from radioactive substance also act as pollutants

There are two types of pollutants:

I. Nondegradable pollutants: The pollutants which are not degraded or degraded at very slov, rate are called Nondegradable pollutants. These are mostly inorganic compounds like metallic oxides. DDT etc.

2. Biodegradable pollutants: The pollutants which are degraded by microorganism are called biodegradable pollutants. These include domestic sewage.

There are different types of pollutions, air, water, soil etc.


The WHO (World Health Organization) defines air pollution in following words. The presence of substances in the atmosphere produced directly or indirectly by man which affect his health and properties is called air pollution.

Burning of the fuel, fossil fuel and waste of different kinds release poisonous gases. These gases are sulphur dioxide, carbon monoxide, hydrogen sulphide, fluorine, chlorine, ammonia, bromine, iodine, nitrogen oxide, ozone etc. Ethylene, acetylene, benzopyrene, propylene and many other hydrocarbons are also released as pollutant. Ethylene is released from automobiles, combustion of natural gas, coal or wood. Millions of tons of poisonous gases are released every year in industrial countries. These gases are produced by factories, electricity power, stations and automobiles.

Types of air pollutants

There are two types of air pollutants:

(a) Primary air pollutants

The substances which are emitted directly from some sources are called primary air pollutants. These include:

  1. Sulphur compounds like SO2, H2S. These gases are produced by the oxidation of fuel.
  1. Carbon compounds like CO, CO, and hydrocarbons. These compounds are produced by incomplete combustion of gasoline.
  2. Nitrogen compounds are NO, NO, and NH3.
  3. Halogen compounds are HF, MCI. These are produced by the industrial processes.
  4. Particles of different sizes suspended in air also act pollutant

(b) Secondary pollutants

The pollutants which are produced by the reactions of primary pollutants in the atmosphere are called secondary pollutants. These reactions may be:

I. Photochemical reactions: These reactions occur between nitrogen

oxide, oxygen and waste carbons in the presence of light. It forms peroxyacetly nitrate (PAN) and ozone 01. Similarly, Chloroflouro carbon (CFC) reacts with ozone layer. It is also a photochemical # reaction. The chlorine of CFC react with 03 and release 0, and atomic oxygen. It causes ozone depletion or ozone hole.

2. Acid rain: In this case, sulphur dioxide (SO2) reacts with rain water to form sulphuric acid sulphuric acid fall on soil with rain. It is called acid rain.

3. Smog: The fog with smokes and chemical fumes forming dark and thick covering called smog. Smog is very common in all industrial countries.

Effects of air pollutants

  1. Effect on plants: Air pollutants have very dangerous effects on plants. Thick smog kills million of trees each year. An air pollutant causes tissue collapse and necrosis. They causes deplasmolysis of the cells. Some pollutants cause chlorosis in the leaves. Thus pale green or yellow patches appear in the leaves. Some pollutants cause shunted growth in plants. Acid rain also destroys different parts of the plants.
  2. Effects on animals and humans: There are certain direct effects of pollutants in animals. They affect on respiratory tract and lungs. They cause pulmonary edema, chronic bronchitis and lung cancer. SO2, NO, and NH3 gases causes irritation in eyes and nose. These are suffocating gases. Carbon mono oxide (CO) is the most dangerous gas It is produced by incomplete combustion of fossil fuel. It reacts with haemoglobin and form a stable compound caroxyhaemoglobin. It decreases the carrying capacity of haemoglobin for oxygen.Industries release many metals in the air like lead and chromium. These metals are carcinogenic. Similarly, some radioactive substance enters into the atmosphere. They also cause cancer.
  1. Green house effect: CO2 is released by the burning of fuel in industries. It forms a layer in the atmosphere. This layer allows the solar radiations to pass. But it does not allow the thermal radiation of earth to pass out. Thus temperature of the earth is continuously rising. It is changing the climatic pattern of the earth. Glaciers are melting rapidly and more evaporation take place form ocean. It causes sever flooding.
  2. Ozone depletion: The photochemical reaction of CFC with Ozone produce ozone hole. Ozone filters most of the ultraviolet radiations. Now these radiations fall on the earth directly. These radiations have very lethal effects on human. They can cause skin cancer and other skin and eye diseases.

Control of air pollution

Following measures can reduce air pollution

  1. High quality lead free petrol should be used It has low sulphur
  2. Use of CNG (Compressed Natural Gas) also reduces the air pollution. It is environment friendly gas.
  3. Two stroke engines should be replaced by four stroke engines. Four stroke engine do not produce CO.
  4. All the industrialists should be bound to install treatment cells in the chimneys of their industries.
  5. CFC gases should be replaced by green gas in refrigerators and air conditioners.


Life is impossible without water. Water is used in different activities like drinking, bathing, disposal of sewage, irrigation and for generating electricity. Undesirable pollutants are added in water. It causes pollution in water.

Sources and effects of water pollution

I. Domestic sewage: It includes household wastes. These wastes have food wastes, detergents and human feces. These wastes are drained into streams and rivers without treatment. Domestic sewage adds nitrogen and phosphate in water. Thus thick bloom of blue green algae is produced on water. It consume:: oxygen at night. Therefore, most of the fishes die due to deficiency of oxygen. There is rapid decomposition of filament of algae. It pr.-duces unpleasant smell. The increased productivity of lake cause• due to enrichment of nutrients is called eutrophication.

  1. Industrial effluents: Industrial waste is called effluents. These are also discharged into the rivers. These wastes come from textile, sugar and fertilizer factories etc. Most of the industrial effluents are toxic. It kills the decomposing bacteria of pond, lake and river. Thus these water bodies become highly contaminated.

The industrial effluents also contain some metals like iron, chromium, mercury, copper and cadmium. These metals cause harmful effects in humans. Mercury produces nervous disorder.

  1. Fertilizers: Artificial fertilizers are used to improve the fertility of soil. Excess fertilizers seep into the ground water or it is carried into the drinking water. Fertilizers are very dangerous for human health. Nitrates of the fertilizers enter into the intestine of man. The intestinal bacteria change them into nitrites. The nitrites enter into the blood. They react with haemoglobin. Therefore, infants face the shortage of oxygen. This disease is galled methohemoglobinemia.
  2. Pesticides and herbicides: Pesticides ,are widely used to kill pests These pesticides are carried away by running wafer into ponds an. rivers. They finally reach the oceans. Some pesticides incorporate into the bodies of plants. The herbivores eat these plants. These pesticides go into their body. Finally herbivores are eaten tiy. human. These pesticides go into human body. The amount of pesticides n increased at each trophie level. It is called biological magnification. Pesticides and herbicides kill many phytoplanktons ant zooplanktons. These also kill many fishes. DDT may cause cance , and nervous disorder in humans.
  3. Mineral oils: Sometimes. oil is discharged into the oceans from oi ships. This oil is not dissolved in water. It is very dangerous for the ocean life.
    Control of water pollution

  1. Sewage should be treated properly before draining it into canals rivers. Sewage treatment plants should be installed in all the cities.
  1. Similarly, the effluents of the industries should be properly treated Laws should be enacted to bind the industrialists to install treatmen plants.
  2. Fertilizers should be used in measured quantities.
  3. Biological control should be preferred over pesticides.


Population is increasing day by day. Therefore, large area of land becoming contaminated. There are different causes of contamination K land. There are folloss Mg sources of land Pollution:

  1. Industrial wastes: Inc industries dispose off 165 million tone mil waste each year. The major sources of land pollution are cemen glass, fiber glass, paper industries. The solid wastes of the. industries are deposited on the land. They make the land unlit 11. cultivation. The solid wastes or cement and textile industries cause lung diseases.
  1. Agricultural pollution: The solid v‘astes of cement and papt. industries deposits on soil. They damage the plants.
  2. Domestic pollution: Domestic pc-210*am includes broken appliance. polythene bags, broken plastic. household garbage. animal waste and glass wares. These pollutants destroy the natural beauty.


Any unwanted sound is called noise. The dumping of unwantec

sound into atmosphere is called noise pollution. Our county is facing the problem of urbanization mid industrialization. Number of industries has been established in cites. These industries and vehicle produce a lot noise. Most the houses, schools and hospitals are located near noise pollutecrareas. Noise affects them badly.

Effects of noise pollution

Constant noise destroys man mentally and physically. It contracts the blood vessels. The skin becomes pale. Adrenaline is released as a result of noise pollution. It raises blood pressure. It also causes hypertension. High intensity sounds cause deafness. It causes headache, fatigue and nausea. It also affects the pregnant woman.

Topic 8: Grey Matter

-Very dine DENDRITES conduct impulses towards the cell body.

-a single long process, the AXON, transmits impulses away from the cell body.

The axons of some motor neurones can be extremely long, such as those that run the full length of the leg.

They can have a large number of connections with other nerve cells.

2) Sensory neurones conduct a nerve impulse to the CNS along a sensory pathway.

3) Sensory neurones enter the spinal cord through dorsal route.

4) Sensory neurone forms a synapse with a relay neurone.

5) Relay neurone forms a synapse with a motor neurone that leaves the spinal cord through the ventral route.

A sensory neurone connects to a range of neurones within the CNS and passes impulses to the brain to produce a coordinated response.

These are both controlled by the autonomic nervous system.

The radial muscles are like the spokes of a wheel and are controlled by a sympathetic reflex. The circular muscles are controlled by a parasympathetic reflex.

2) This causes a nerve impulse

3) The nerve impulse is passed along the optic nerve

4) One of sites it passes is a set or coordinating cells in the midbrain.

5) Impulses from these cells are sent through parasympathetic motor neurones.

6) The impulse is sent to the muscles (circular) in the iris.

7) Circular muscles will contract.

8) Radial will relax, pupil constricts

-Axons are generally only 1 axon per cell whereas there are usually many dendrites per cell

-Axons can have myelin whereas Dendrites do not have insulation

2) The electrical gradient due to the difference in charge on the two sides of the membrane resulting from K+ diffusion.

2) The potential difference across the axon membrane is created by the distribution of charged ions. There are several factors which affect the movement of ions.

3) Sodium-potassium pumps in the axon membrane transport 3 sodium ions (Na+)out of the axon, for every 2 potassium ions (K+) it moves inside, using active transport.

K+ ions will diffuse out of the axon - down the concentration gradient. As K+ ions move out they transfer positive charge from the inside to the outside.

The negative state inside the axon produces an electro-chemical gradient, causing K+ ions to be attracted to the inside of the axon.

THE K+ CONCENTRATION FORCE IS GREATER THAN THE ELECTROCHEMICAL FORCE. This results in an overall movement of K+ ions out of the axon, causing the outside to be more positive than inside.

-If an electrical current above a THRESHOLD level is applied to the membrane, it causes a massive change in the potential difference. The potential difference across the membrane is locally reversed, making the inside of the axon positive and the outside negative. This is known as DEPOLARISATION.

-The potential difference becomes +40mV or so for a very brief instant, lasting about 3 milliseconds (ms), before returning to the resting state, as shown by the oscilloscope trace.

When a neurone is stimulated some depolarisation occurs. The change in the potential difference across the membrane causes a change in the shape of the Na+ gate, opening some of the voltage-dependent sodium ion channels. As the sodium ions flow in, depolarisation increases, triggering more gates to open once a certain p.d. threshold is reached. The opening of more gates increases depolarisation further.

This is an example of positive feedback - a change encourages further change of the same sort - and it leads to a rapid opening of all of the Na+ gates.

There is a higher concentration of sodium ions outside of the axon, so sodium ions flow rapidly inwards through the open voltage-dependent Na+ channels, causing a build-up of positive charges inside. This reverses the polarity of the membrane. The potential difference across the membrane reaches +40mV.

-After about 0.5ms, voltage-dependent Na+ channels spontaneously close and Na+ permeability of the membrane returns to it's usual very low level.

-Voltage-dependent K+ channels open due to the depolarisation of the membrane. As a result, K+ ions move out of the axon, down the electrochemical gradient (they diffuse down the concentration gradient and are also attracted by the negative charge outside the cell surface membrane).

-The membrane is now highly permeable to potassium ions and more ions move out than occurs at resting potential, making the potential difference more negative than the normal resting potential.

A stimulus will be below the threshold value if insufficient numbers of sodium channels open, preventing full depolarisation of the axon.

1 hour = 3600000miliseconds

-due to increased permeability of Na+ ions / (voltage gated) sodium channels open (1)

-(followed by) an increased permeability to potassium ions / potassium channels open (1)

-They form synapses with other neurones

As part of the membrane becomes depolarised at the site of an action potential, a local electrical current is created as the charged sodium ions flow between the depolarised part of the membrane and the adjacent resting region.


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