Impacts of Light Pollution on the Environment

All life evolved with predictable daily, monthly, and seasonal patterns of light and dark, and these patterns regulate the natural rhythms and processes of nearly every living being. Artificial light at night and light pollution change the natural patterns of light and dark, which in turn alters the behaviour and ecological relationships of many plant and animal species.

Migration

Many birds migrate at night, and are often confused by brightly lit buildings and communication towers. Hundreds of millions of birds die from collisions with infrastructure in North America every year [1]. Birds are also vulnerable to confusion by lights offshore, where they often collide with cruise ships, lighthouses, fishing vessels, oil derricks, and lighted buoys [2].

Lighting also influences the migration of marine organisms in and out of wetlands and streams, up and down rivers, and vertical migration within a water body. Aquatic invertebrates like zooplankton, for example, migrate up and down in water as light levels change, foraging near the surface only during dark conditions to avoid predation. Changes in surface lighting, such as an increase in artificial light at night, can disrupt this vertical migration, which can lead to a buildup of algae and deterioration of water quality and ecosystem health [2].

Navigation

Animals that are active during the night rely on natural light patterns for navigation. The land horizon is naturally darker than the water horizon because of reflections from the moon and stars on water bodies. Many organisms use this pattern of light to orient themselves and navigate. Artificial light from buildings, roadways, and billboards makes the land horizon brighter than the water horizon, reversing the natural pattern that many species depend on [2].

Sea turtles commonly become disoriented by artificial lights, and may wander onto nearby roadways and risk being hit by vehicles. Sea turtle hatchlings are also disoriented by artificial light; they use the natural light patterns of the land and water horizons to navigate toward the safety of the sea, and may mistakenly navigate toward inland sources of artificial light instead, where they are more vulnerable to predation and will likely never reach the sea [1].

Nesting

Artificial light at night can influence the nesting behaviour of animals like sea turtles and birds. Female sea turtles commonly avoid nesting on beaches that are brightly illuminated [1], and birds may avoid nesting sites that are near to light sources [2]. Park managers in California’s Channel Islands National Park also observed higher rates of nest abandonment among seabirds in areas where fishing boats equipped with bright dusk-to-dawn floodlights were present [2].

Foraging, feeding, and activity

Additional light at night increases the foraging efficiency of predators by making it easier for them to find prey. In this way, artificial light at night affects predator-prey relations. Prey animals may reduce their foraging activity in brightly illuminated areas to lower their risk of predation, giving them less time to find the amount of food they need [2].

Nocturnal seabirds are generally less active on moonlit nights, and those that are active face higher rates of predation. In 1999, Channel Islands National Park, off the southern coast of California, saw a dramatic increase of fishing boats equipped with dusk-to-dawn floodlights to attract squid. That year, death rates of nocturnal seabirds doubled. Park managers believed that the seabirds, without the safety of darkness, were subjected to higher than normal predation. The area was then closed to squid boats, and death rates returned to normal [2].

Frogs and amphibians are very sensitive to changes in ambient illumination, and a flash of headlights is enough to stop their activity for hours. Some amphibians will only forage in extremely low light levels [2].

Many animals also have specific illumination preferences based on physiological requirements. For example, animals living in desert habitats with extreme daytime temperatures may be more active during the night, when temperatures are lower. Artificial light after dark may further delay the emergence and activity of these animals [2].

Development, reproduction, and survival

Artificial light at night may affect the development of some species. Studies have shown that light influences the developmental rates of amphibians [2].

Light also impacts communicative and mating behaviours. Frogs inhibit their mating calls when exposed to excessive light at night, which decreases their reproductive capacity. Fireflies use their lights for communication and mating. Artificial light washes out their signals and may contribute to their decline, as well as the decline of other species who rely on bioluminescent illumination [2]. Many marine species, including corals, are highly sensitive to light and synchronize spawning according to lunar cycles. Additional light alters the natural lunar light patterns and disrupts the reproductive cycle of these species [3].

Light can also be important in determining when species react to seasonal changes. Disrupting these reactions can put the species out of phase with climate, and may result in them being unprepared for seasonal transitions [2].

Plants

Plants also rely on light levels to regulate natural processes and rhythms. Prolonged exposure to artificial light at night prevents many trees from adjusting to seasonal variations, leaving them unprepared for seasonal changes in weather and temperature. This, in turn, has implications for the wildlife that depend on those trees for their habitat [1]. 

Artificial light at night also disrupts nocturnal pollination networks [6], which has negative consequences for the reproductive success of plants. One study found that plants in artificially illuminated areas received 62% fewer visits from nocturnal pollinators throughout the night than plants in dark areas [5].

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[1] Chepesiuk R. Missing the dark: health effects of light pollution. Environ Health Perspect. 2009: 117(1):A20-A27. doi:10.1289/ehp.117-a20

[2] Longcore, T., Rich, C. Artificial Night Lighting and Protected Lands: Ecological Effects and Management Approaches. Natural Resource Report NPS/NRSS/NSNS/NRR—2016/1213. 2016.

[3] Davies, T.W., Duffy, J.P., Bennie, J., Gaston, K.J. The nature, extent, and ecological implications of marine light pollution. Front Ecol Environ 2014; 12(6): 347–355, doi:10.1890/130281

[4] Jägerbrand, A.K., Bouroussis, C.A. Ecological Impact of Artificial Light at Night: Effective Strategies and Measures to Deal with Protected Species and Habitats. Sustainability 2021: 13, 5991. https://doi.org/10.3390/su13115991

[5] Knop, E., Zoller, L., Ryser, R. et al. Artificial light at night as a new threat to pollination. Nature 548, 206–209 (2017). https://doi.org/10.1038/nature23288