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Ecological light pollution [1] is the effect of artificial light on individual organisms and on the structure of ecosystems as a whole.
The effect that artificial light has upon organisms is highly variable, [2] and ranges from beneficial (e.g. increased ability for predator species to observe prey) to immediately fatal (e.g. moths that are attracted to incandescent lanterns and are killed by the heat). It is also possible for light at night to be both beneficial and damaging for a species. As an example, humans benefit from using indoor artificial light to extend the time available for work and play, but the light disrupts the human circadian rhythm, and the resulting stress is damaging to health. [3] [4]
Through the various effects that light pollution has on individual species, the ecology of regions is affected. In the case where two species occupy an identical niche, the population frequency of each species may be changed by the introduction of artificial light if they are not equally affected by light at night. For example, some species of spiders avoid lit areas, while other species willingly build webs directly on lamp posts. Since lamp posts attract many flying insects, [5] the spiders that tolerate light gain an advantage over the spiders that avoid it, and may become more dominant in the environment as a result. [6] Changes in these species frequencies can then have knock-on effects, as the interactions between these species and others in the ecosystem are affected and food webs are altered. These ripple effects can eventually affect diurnal plants and animals. As an example, changes in the activity of night active insects can change the survival rates of night blooming plants, [7] which may provide food or shelter for diurnal animals.
The introduction of artificial light at night is one of the most drastic anthropogenic changes to the Earth, comparable to toxic pollution, land use change, and climate change due to increases in the concentration of green house gases.
The introduction of artificial light disrupts several natural light cycles that arise from the movements of the Earth, Moon, and Sun, as well as from meteorological factors.
The most obvious change in introducing light at night is the end of darkness in general. The day/night cycle is probably the most powerful environmental behavioral signal, as almost all animals can be categorized as nocturnal or diurnal. If a nocturnal animal is only active in extreme dark, it will be unable to survive in lit areas. The most acute affects are directly next to streetlights and lit buildings, but the diffuse light of skyglow can extend out to hundreds of kilometers away from city centres.
The axial tilt of the Earth results in seasons outside of the tropics. The change in the length of the day, or photoperiod, is the key signal for seasonal behavior (e.g. mating season) in non-tropical animals and plants. The presence of light at night can result in "seasons out of time", [8] changing the behavior, thermoregulation, and hormonal functioning of affected organisms. This may result in a disconnect between body functioning and seasonality, causing disruptions to reproduction, dormancy, and migration.
The behavior of some animals (e.g. coyotes, [9] bats, [10] toads, [11] insects) is keyed to the lunar cycle. Near city centers the level of skyglow often exceeds that of the full moon, [12] so the presence of light at night can alter these behaviors, potentially reducing fitness.
In pristine areas, clouds blot out the stars and darken the night sky, resulting in the darkest possible nights. In urban and suburban areas, in contrast, clouds enhance the effect of skyglow, [12] particularly for longer wavelengths. [13] This means that the typical level of light is much higher near cities, but it also means that truly dark nights never occur in these areas.
The attraction of insects to artificial light is one of the most well known examples of the effect of light at night on organisms. When insects are attracted to lamps they can be killed by exhaustion or contact with the lamp itself, and they are also vulnerable to predators like bats. [5]
Insects are affected differently by the varying wavelengths of light, and many species can see ultraviolet and infrared light that is invisible to humans. Because of variances in perception, moths are more attracted to broad spectrum white and bluish light sources than they are to the yellow light emitted by low pressure sodium-vapor lamps. [14]
The compound eye of moths results in fatal attraction to light. [15]
Dragonflies perceive horizontally polarized light as a sign of water. For this reason, sources of water are indistinguishable from asphalt roads with polarized light pollution to them. Dragonflies searching for water either to drink or in which to lay eggs often land on roads or other dark flat reflective surfaces such as cars and remain there until they die of dehydration and hyperthermia. [16]
Light pollution may hamper the mating rituals of fireflies, once they depend on their own light for courtship, resulting in decreased populations. [17] [18] [19]
Fireflies are charismatic (which is a rare quality amongst insects) and are easily spotted by nonexperts, providing thus good flagship species to attract public attention; good investigation models for the effects of light on nocturnal wildlife; and finally, due to their sensibility and rapid response to environmental changes, good bioindicators for artificial night lighting. [20]
Lights on tall structures can disorient migrating birds leading to fatalities. An estimated 365-988 million fatal bird collisions with buildings occur annually in North America, making human-made structures a large contributor to the decline in bird species. [21] The surface area of glass emitting artificial light at night is a major factor for fatal bird collisions with buildings, and turning off lights at night can minimize these fatalities. [22] The Fatal Light Awareness Program (FLAP) works with building owners in Toronto, Canada and other cities to reduce mortality of birds by turning out lights during migration periods.
Similar disorientation has also been noted for bird species migrating close to offshore production and drilling facilities. Studies carried out by Nederlandse Aardolie Maatschappij b.v. (NAM) and Shell have led to development and trial of new lighting technologies in the North Sea. In early 2007, the lights were installed on the Shell production platform L15. The experiment proved a great success since the number of birds circling the platform declined by 50–90%.[56] Juvenile seabirds may also be disoriented by lights as they leave their nests and fly out to sea causing events of high mortality. [23] To minimise mortality rescue programs are conducted on many islands giving a second chance to thousands of seabird fledglings. [24]
Birds migrate at night for several reasons. Save water from dehydration in hot day flying and part of the bird's navigation system works with stars in some way. With city light outshining the night sky, birds (and also about mammals) no longer navigate by stars. [25]
Ceilometers (searchlights) can be particularly deadly traps for birds, [26] as they become caught in the beam and risk exhaustion and collisions with other birds. In the worst recorded ceilometer kill-off, on October 7–8, 1954, 50,000 birds from 53 different species were killed at Warner Robins Air Force Base. [27]
Lights from seashore developments repel nesting Sea turtle mothers, and their hatchlings are fatally attracted to street and hotel lights rather than to the ocean. [28]
Artificial lighting has many negative impacts on trees and plants, particularly in fall and autumn phenology. Trees and herbaceous plants rely on the photoperiod, or the amount of time in a day where sunlight is available for photosynthesis, to help determine the changing seasons. When the hours of sunlight decrease, plants can recognize that autumn is underway and begin to make preparations for winter dormancy. For example, deciduous trees shift the colour of their leaves to maximize different wavelengths of light that are more prevalent in the fall before eventually dropping them as light becomes too scarce for photosynthesis to be worthwhile. When deciduous trees are exposed to light pollution, they mistake the artificial light for sunlight and retain their green leaves later into the autumn season. This can be dangerous for the tree, as it wastes energy trying to photosynthesize that should be preserved for winter survival. Light pollution can also cause leaf stoma to remain open into the night, which leaves the tree vulnerable to infection and disease. [29]
Similarly, light pollution in the spring can also be dangerous for trees and herbaceous plants. Artificial light causes plants to think that spring has arrived and it is time to begin producing leaves for photosynthesizing again. However, temperatures may not yet be warm enough to support the new leaf buds, and they are susceptible to frost, which can impair future leaf production. Small herbaceous plants that are exposed to artificial lighting potentially face a greater risk, as more of their body is illuminated. Therefore, only the root system is protected, and could potentially not be enough to sustain the whole plant as it tries to remain green through the fall and winter. [30]
Ecological light pollution has also critical effects on marine ecosystems. [31]
Zooplankton (e.g. Daphnia) exhibit diel vertical migration. That is, they actively change their vertical position inside of lakes throughout the day. In lakes with fish, the primary driver for their migration is light level, because small fish visually prey on them. The introduction of light through skyglow reduces the height to which they can ascend during the night. [32] Because zooplankton feed on the phytoplankton that form algae, the decrease in their predation upon phytoplankton may increase the chance of algal blooms, which can kill off the lakes' plants and lower water quality.
Light pollution impacts migration in some species of fish. For example, juvenile chinook salmon are attracted to and slowed down by artificial light. It is possible that artificial light draws them closer to the shoreline, where they face a greater risk of predation from birds and mammals. Artificial lighting also attracts a greater density of piscivorous fish, which have an advantage due to the slower movement of the juvenile fish. [33] Light pollution also has impacts on the hormonal functioning of some fish; European perch and roach both experience reductions in the production of reproductive hormones when exposed to artificial lighting in a rural environment. [34] Artificial light has also been shown to cause disruptions to fish (and zooplankton) in the high Arctic, where fishing boats with lights resulted in a lack of fish up to 200 metres below the water's surface. [35]
At the turn of the century it was discovered that human eyes contain a non-imaging photosensor that is the primary regulator of the human circadian rhythm. [36] This photosensor is particularly affected by blue light, and when it observes light the pineal gland stops the secretion of melatonin. The presence of light at night in human dwellings (or for shift workers) makes going to sleep more difficult and reduces the overall level of melatonin in the bloodstream, and exposure to a low-level incandescent bulb for 39 minutes is sufficient to suppress melatonin levels to 50%. [4] [37] Because melatonin is a powerful anti-oxidant, it is hypothesized that this reduction can result in an increased risk of breast and prostate cancer. [38] [39]
Other human health effects may include increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety. [40] [41] [42] [43] Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effect on mood and anxiety. [44] [45]
The effect that artificial light has upon organisms is wavelength dependent. While human beings cannot see ultraviolet light, it is often used by entomologists to attract insects. Generally speaking, blue light is more likely to be damaging to mammals because the non-imaging photoreceptors in mammalian eyes are most sensitive in the blue region. [46] This means that if traditional vapor discharge streetlamps are replaced by white LEDs (which generally emit more of their radiation in the blue part of the spectrum), the ecological impact could be greater even if the total amount of radiated light is decreased. [47]
Artificial planar surfaces, such as glass windows or asphalt reflect highly polarized light. Many insects are attracted to polarized surfaces, because polarization is usually an indicator for water. This effect is called polarized light pollution, [48] and although it is certainly a form of ecological photopollution, "ecological light pollution" usually refers to the impact of artificial light on organisms.
In the night, the polarization of the moonlit sky is very strongly reduced in the presence of urban light pollution, because scattered urban light is not strongly polarized. [49] Since polarized moonlight is believed to be used by many animals for navigation, this screening is another negative effect of light pollution on ecology.
To regulate and manage the problem of light pollution, it needs to establish a mature management system. Based on Zhou's studies, posing regulations such as green lighting, strengthening the propaganda and education by governors could help stop or reduce the adverse impacts of light pollution. [50]
Light pollution is the presence of any unwanted, inappropriate, or excessive artificial lighting. In a descriptive sense, the term light pollution refers to the effects of any poorly implemented lighting sources, during the day or night. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind of pollution, but also as a contributor to the wider, collective impact of various sources of pollution.
Nocturnality is a behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite.
Moths are a group of insects that includes all members of the order Lepidoptera that are not butterflies. They were previously classified as suborder Heterocera, but the group is paraphyletic with respect to butterflies and neither subordinate taxon is used in modern classifications. Moths make up the vast majority of the order. There are approximately 160,000 species of moth, many of which have yet to be described. Most species of moth are nocturnal, although there are also crepuscular and diurnal species.
Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylight. Daylighting is sometimes used as the main source of light during daytime in buildings. This can save energy in place of using artificial lighting, which represents a major component of energy consumption in buildings. Proper lighting can enhance task performance, improve the appearance of an area, or have positive psychological effects on occupants.
Urban ecology is the scientific study of the relation of living organisms with each other and their surroundings in an urban environment. An urban environment refers to environments dominated by high-density residential and commercial buildings, paved surfaces, and other urban-related factors that create a unique landscape. The goal of urban ecology is to achieve a balance between human culture and the natural environment.
Since the 1980s, decreases in amphibian populations, including population decline and localized mass extinctions, have been observed in locations all over the world. This type of biodiversity loss is known as one of the most critical threats to global biodiversity. The possible causes include habitat destruction and modification, diseases, exploitation, pollution, pesticide use, introduced species, and ultraviolet-B radiation (UV-B). However, many of the causes of amphibian declines are still poorly understood, and the topic is currently a subject of ongoing research.
Skyglow is the diffuse luminance of the night sky, apart from discrete light sources such as the Moon and visible individual stars. It is a commonly noticed aspect of light pollution. While usually referring to luminance arising from artificial lighting, skyglow may also involve any scattered light seen at night, including natural ones like starlight, zodiacal light, and airglow.
The dark-sky movement is a campaign to reduce light pollution. The advantages of reducing light pollution include an increased number of stars visible at night, reducing the effects of electric lighting on the environment, improving the well-being, health and safety of people and wildlife, and cutting down on energy usage. Earth Hour and National Dark-Sky Week are two examples of such efforts.
International Dark Sky Week is held during the week of the new moon in April, when people worldwide may turn off their lights to observe the beauty of the night sky without light pollution. This event was founded in 2003 by high school student Jennifer Barlow of Midlothian, Virginia. It has been endorsed by the International Dark-Sky Association, the American Astronomical Society, the Astronomical League, and Sky & Telescope.
The Barolo shearwater, also known as the North Atlantic little shearwater or Macaronesian shearwater, is a small shearwater which breeds in the Azores and Canaries of Macaronesia in the North Atlantic Ocean. The English name and the specific baroli refers to Carlo Tencredi Falletti, marquis of Barolo.
Sensory ecology is a relatively new field focusing on the information organisms obtain about their environment. It includes questions of what information is obtained, how it is obtained, and why the information is useful to the organism.
Bird–window collisions are a problem in both low- and high-density areas worldwide. Birds strike glass because reflective or transparent glass is often invisible to them. It is estimated that between 100 million and 1 billion birds are killed by collisions in the United States annually, and an estimated 16 to 42 million birds are likewise killed each year in Canada.
Ecological traps are scenarios in which rapid environmental change leads organisms to prefer to settle in poor-quality habitats. The concept stems from the idea that organisms that are actively selecting habitat must rely on environmental cues to help them identify high-quality habitat. If either the habitat quality or the cue changes so that one does not reliably indicate the other, organisms may be lured into poor-quality habitat.
Light effects on circadian rhythm are the response of circadian rhythms to light.
An LED street light or road light is an integrated light-emitting diode (LED) light fixture that is used for street lighting.
Globe at Night is an international scientific research program that crowdsources measurements of light pollution in the night sky. At set time periods within each year, the project asks people to count the number of stars that they can see from their location and report it to the project's website. The coordinating researchers compile this information to produce a public, freely available map of global light pollution. By September 2011, almost 70,000 measurements had been made. The use of data collected by the public makes the program an example of citizen science. Globe at Night began as a NASA educational program in the US organized by the NOAO, and was expanded internationally during the 2009 International Year of Astronomy; it is an offshoot of the GLOBE Program, which focuses on school-based science education.
Migrating birds face many perils as they travel between breeding and wintering grounds each year.
Pollutant-induced abnormal behaviour refers to the abnormal behaviour induced by pollutants. Chemicals released into the natural environment by humans impact the behaviour of a wide variety of animals. The main culprits are endocrine-disrupting chemicals (EDCs), which mimic, block, or interfere with animal hormones. A new research field, integrative behavioural ecotoxicology, is emerging. However, chemical pollutants are not the only anthropogenic offenders. Noise and light pollution also induce abnormal behaviour.
The spectral G-Index is a variable that was developed to quantify the amount of short wavelength light in a visible light source relative to its visible emission. The smaller the G-index, the more blue, violet, or ultraviolet light a lamp emits relative to its total output. It is used in order to select outdoor lamps that minimize skyglow and ecological light pollution. The G-index was originally proposed by David Galadí Enríquez, an astrophysicist at Calar Alto Observatory.
Light pollution is the presence of unwanted artificial light that brightens the night sky. Improperly shielded lights are the source of many of the issues regarding the light pollution in Hawai'i. Urban centers in the cities are often so bathed in light that over a hundred kilometers from the city's edge, the light pollution resulting from the glow is present. Fabio Falchi is quoted as stating that “light pollution is one of the most pervasive forms of environmental alteration” due to its destructive nature in both un- and protected areas such as national parks. Dark night skies are an important natural, cultural, scientific, educational, and economic resource for Hawai‘i.