When the night disappears: Why light pollution contributes to species extinction

When night falls, the day begins for many animals: bats go hunting for insects, frogs start their mating calls— and moths take on an often overlooked role in the ecosystem. They pollinate flowers that are specifically adapted to nocturnal pollinators: these plants open only in the evening and deliberately attract them with intense scents and bright colors.

But this finely tuned interplay is increasingly falling out of sync. Artificial light at night not only disrupts the orientation of moths, but also affects numerous nocturnal animals: bats avoid illuminated areas, amphibians stop their courtship behavior, migratory birds are led astray. Plants, too, can be affected—for example through shifted flowering times or disrupted activity of their nocturnal pollinators. Light pollution changes life rhythms, disrupts ecological networks—and thus endangers entire species.

While air pollution has long entered public awareness, light pollution often goes unnoticed—yet today it is one of the underestimated but influential drivers of species extinction. Every new streetlamp, every glowing billboard, every permanently lit terrace displaces the last dark refuges for nocturnal animals. Fireflies can hardly be seen anymore in many places—even my last encounter with them was a long time ago.

What is light pollution?

Darkness really belongs to Earth just as naturally as daylight. But in our modern world, it no longer gets properly dark at night in many places. Instead, a veil of artificial light spreads over cities, villages and landscapes.

Light pollution means that artificial light appears at the wrong time or in the wrong place and overlays natural darkness. There are different forms of it:

• Skyglow: A glowing dome of light forms above cities and settlements that makes the stars disappear.
• Light trespass: Light penetrates areas that should actually be dark, such as bedrooms, protected areas or gardens.
• Glare: Bright, poorly directed lighting disrupts vision and can impair orientation.
• Clutter: Countless light sources such as illuminated advertisements and decorative lighting compete for attention.

The main sources of this nocturnal brightening are street lighting, industrial facilities, residential buildings, floodlights and advertising boards. Much light is lost unused upward or sideways—where it causes disturbance but provides no benefit.

Light pollution is now a form of environmental pollution that changes Earth’s natural rhythm. Unlike air or water pollution, it would theoretically be reversible immediately: all you would have to do is switch off the unnecessary light. Light pollution is everywhere, but it is hardly perceived consciously.

Earth is getting brighter at night—a global problem

When the sun goes down, darkness should envelop the world. But in many places it remains bright even at night. In 2017, an international research group led by Christopher Kyba showed that artificial illumination of Earth at night continues to increase—both in brightness and in spatial extent.

Between 2012 and 2016 satellite-measured light intensity increased by around 2.2% per year—and so did the illuminated area. In economically booming regions in particular, light intensity even grew by more than 10% per year. In Europe, by contrast, the illuminated area remains largely constant, but the replacement of old lamps by modern blue-rich LEDs still leads to a significantly brighter night sky.

At the same time, satellite measurements underestimate the actual increase in light: sensors such as VIIRS do not adequately capture the intense blue light of LEDs. The real global increase could therefore be significantly higher. Only a few countries—such as Yemen or Syria—recorded a decline in light pollution because of political crises.

A comprehensive survey from 2016 confirms this trend: More than 80% of the world’s population now lives under a light-polluted sky—in Europe and the USA even more than 99%. For more than a third of humanity, the Milky Way is no longer visible—in North America this applies to almost 80% of the population.

Around 23% of the land surface between 75° north and 60° south already experiences significant nighttime light pollution. Particularly worrying is this: the increasing use of white LEDs can raise the brightness of the night sky in the blue spectral range two- to threefold—precisely in the range that is most disruptive for many animals.

Why is light pollution a problem for biodiversity?

For many living beings, the darkness of night is vital. The natural alternation of light and dark determines foraging, reproduction, orientation and migratory movements. But artificial light disrupts these processes—with serious consequences for entire ecosystems:

• Insects are attracted in large numbers to light sources, become exhausted or become easy prey. Moths, fireflies or glow-worms, dipterans (mosquitoes, flies) and hymenopterans (such as nocturnal wasps) are particularly affected.
• Migratory birds lose their orientation by the stars, are misled by light and often collide with illuminated buildings.
• Amphibians such as frogs and toads call less often or not at all under artificial light—which severely impairs reproduction.
• Bats react differently: light-averse species avoid illuminated areas and lose important hunting grounds, while more light-tolerant species spread.
• Plants experience shifted flowering times, extended photosynthesis or disrupted leaf-shedding rhythms because of permanent illumination.

In addition, the biological clock—the circadian rhythm—gets out of balance in many species. Not only individual animals, but whole ecological networks are destabilized.

Some species affected by light pollution

These examples show how diverse the effects of light pollution can be on different animal species:

Ocelots & pumas

Cats such as ocelots (Leopardus pardalis) and pumas (Puma concolor) are perfectly adapted to nocturnal lifestyles: with rotatable ears, light-amplifying eyes and a keen sense of smell, they are highly specialized hunters. But artificial light throws their abilities out of balance.

A study (2022) from Panama showed that ocelots avoid illuminated areas and are markedly less active at night near human settlements. The greater the distance from human light sources, the more often ocelots were observed at night. In heavily settled areas, some animals even shifted part of their activity into daytime—an indication of disturbed internal clocks.

Pumas in the USA also avoid strongly illuminated areas, according to a study (2023), which can restrict their home ranges and endanger genetic exchange. In Southern California, it became clear that lights within a radius of around 500 meters in particular strongly influence how pumas use space.

For nocturnal hunters, light means not only greater visibility to prey animals, but also stronger competition and an increased risk of being detected themselves. Artificial light can also disrupt mating activity and alter territorial behavior. Particularly problematic is that in fragmented landscapes, roads and settlements create illuminated barriers that separate important habitats from one another. Protecting dark corridors is essential.

Baird’s tapir

The Baird’s tapir (Tapirus bairdii) is the largest land mammal in Central America and a keystone organism of tropical forests: it disperses seeds and shapes vegetation in a lasting way.

Tapirs need large, undisturbed areas. Light pollution threatens them in several ways: in Mexico, a study (2020) showed that tapirs are active mainly on dark nights and during the darkest hours—especially in areas with human presence. Under illumination or during brighter moon phases, they remain hidden for longer.

Modern LED flashlights exacerbate the problem: because tapirs freeze when suddenly dazzled, this behavior greatly facilitates poaching. A study (2020) shows that in some regions poaching has increasingly shifted into the night because of powerful flashlights—with dramatic consequences for populations.

Barbastelle bat

The western barbastelle (Barbastella barbastellus) is one of Europe’s most light-sensitive bat species. It prefers old, structurally rich forests—habitats that are increasingly disappearing because of forestry and light pollution.

In a study (2021), animals were fitted with radio trackers to examine their roosts more closely. The results were clear: western barbastelles specifically sought out dark hiding places—either under loose bark or in crevices of dark, unlit barns.
Even on buildings, they preferred the sides facing away from light. Even weak illumination acts like an invisible barrier and can make hunting grounds and movement corridors impassable. For the conservation of this species, connected, low-light landscapes are crucial.

Common toad

Amphibians such as the common toad (Bufo bufo) also depend on nighttime darkness—artificial light throws their internal rhythms out of balance. In an experimental study (2019), even low light intensity (5–20 lux) reduced the nighttime activity of males during the breeding season by up to 73%.

Total energy intake remained stable, but the allocation of energy changed: basal metabolic rate rose, indicating physiological stress—presumably because of elevated corticosterone levels. Such disturbances can greatly reduce reproductive chances, especially because common toads have only a short window of time for mating.

Tawny Owl

The tawny owl (Strix aluco) is one of the most common owl species in Central Europe—but even it suffers from light pollution. As a nocturnal hunter with light-sensitive eyes, it avoids artificially illuminated areas, which severely restricts its hunting opportunities in urbanized landscapes.

A study from Italy (2023) investigated the influence of urban factors such as traffic noise, development and artificial light at night (ALAN) on the occurrence of the tawny owl. The result: not noise or building density, but light pollution was the strongest predictor of the birds’ absence—even in areas with suitable habitats.

These results suggest that artificial light is a central disturbance factor for the distribution of this bird species. Its absence from illuminated urban areas illustrates how strongly nocturnal species are restricted in their use of habitat by ALAN—with potential consequences for their survival in urban ecosystems.

Little Penguin

The little penguin (Eudyptula minor) is the smallest member of its family and unique among the 18 penguin species: it is predominantly nocturnal. At night it returns from foraging to land, uses individual calls to find its partner and moves along fixed “penguin paths” to the nests.

But this adaptation makes little penguins especially vulnerable to light pollution. Research shows that artificial light on breeding islands changes return behavior: Little Penguins come ashore later, vocalize less and are observed less often—especially when bright white light from flashlights or smartphones is used. In a long-term observation on Granite Island (South Australia), nighttime illumination correlated with a lower presence of the animals on land. The effect was particularly pronounced in combination with other disturbances such as dogs or loud events.

Because the animals breed at night and care for their young, a delayed return to the nest can have negative consequences for breeding success. A study (2023) also shows that chronic disturbance by light and human activities can lead in the long term to stress, energy loss and a decline in colony size. The protection of dark breeding areas, clear rules for visitors and conscious light management are important for the survival of the little penguin.

Light pollution in water: an often overlooked problem

Not only on land, but also underwater, artificial light has serious consequences. A study by Maja Grubisic et al. (2018) showed that LED lighting along drainage ditches changes the activity and composition of algae. Algae are at the base of many food webs—if their development is disturbed, this can have far-reaching consequences for the entire aquatic ecosystem. Nocturnal fish, crustaceans and insects also react sensitively: light disrupts their orientation, alters migratory movements and makes foraging more difficult.

Another study by Matthew Garratt et al. (2019) demonstrated that in illuminated coastal zones, the number of small invertebrates such as amphipods or bristle worms declines. Yet these are essential food for shorebirds such as sandpipers or plovers. If these prey animals are missing, the birds’ condition deteriorates—with consequences for their migratory ability, survival and reproduction.

What effects does artificial light at night have on insects?

A review study by Avalon C. S. Owens and Sara M. Lewis (2018) analyzed more than 150 research papers on the influence of artificial light on nocturnal insects. The result: light pollution is a serious environmental stressor—with a wide range of consequences. The effects can be summarized in four main categories:

1. Behavioral changes

Many insects are attracted to light sources and circle there for hours instead of foraging or reproducing.
Others avoid illuminated areas completely, which limits their distribution and activity.
Many lose their natural rhythm because of light and miss ecological “time windows”—for example for reproduction.

2. Disruptions to reproduction and communication

Fireflies, which use light signals to find mates, can no longer find one another in the sea of lights of modern cities.
Even scent signals (pheromones) are perceived or produced less effectively under light stress.

3. Physiological effects

Artificial light influences the circadian rhythm of insects.
Nighttime illumination can lead to delayed development, altered hormone production or increased mortality. The ability to regulate temperature is also impaired.

4. Ecological consequences

Predators such as bats or birds lose prey, or the composition of insect species shifts.
Plants that depend on nocturnal pollinators produce fewer fruits or seeds.

Light pollution affects not only nocturnal but also diurnal insects: a study (2024) shows that constant artificial light disrupts the natural sleep rhythm of honey bees, leading to reduced sleep duration and more disturbances in social behavior. Because healthy sleep is essential in bees for learning and orientation processes as well as communication in the hive, such disruptions could in the long term impair foraging efficiency and the pollination performance of entire bee colonies—with potential impacts on the whole plant world.

Light pollution—a danger not only for animals and plants

Light pollution is not only an ecological problem, but also affects our energy balance and health. It increases CO₂ emissions, disrupts human sleep and has been linked to an elevated risk of various cancers.

A global analysis (2016) showed clear correlations between the intensity of nighttime illumination and the incidence of breast, lung, colorectal and prostate cancer. In strongly illuminated regions, cancer risk was significantly increased. It is suspected that suppression of the sleep hormone melatonin and disruption of the natural day-night rhythm play a role.

A current study (2025) also examined the effects on children: babies who were exposed to heavy light pollution before or shortly after birth—for example because of street lighting in residential areas—could have an increased risk of childhood thyroid cancer. The early developmental phase seems to be particularly sensitive, when the body and organs are highly vulnerable to disturbances.

These findings show that light pollution threatens not only flora and fauna, but can also affect human health—especially that of children. Reducing light emissions in a targeted way can therefore only help—for the protection of nature and public health.

What can we do?

Technical and design measures

• Use warm white light with a low blue component (<3,000 Kelvin)—blue-rich light is particularly disruptive for insects and the human sleep-wake rhythm.
• Design luminaires so that they emit light only downward in order to avoid stray light.
• Install motion sensors and timers to reduce unnecessary permanent lighting.
• Near bodies of water or natural areas, mount light sources as low as possible to minimize the spread of light.

Political measures

• Develop municipal lighting concepts and light management plans that take into account both traffic safety and the protection of the night.
• For construction projects and infrastructure measures, specifically plan for the effects on nocturnal animals.
• Protect conservation areas from light pollution not only during the day, but also at night.

Private initiatives

• Avoid unnecessary lighting—especially solar lights, fairy lights and permanent garden lighting.
• Mow less and allow natural vegetation—this supports fireflies as well as hedgehogs, bats and owls.
• Take part in citizen science projects such as the Firefly Atlas and report sightings of fireflies in order to provide important data for conservation.

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Light pollution is a silent, often overlooked danger for many species. But unlike other environmental problems, the solutions are quick and easy to implement—if the will is there. What is needed is intelligent, environmentally sound lighting and a new awareness of the importance of the night. Because only those who know darkness can truly appreciate light.

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Studies mentioned

• Al-Naggar, R. A., & Anil, S. (2016). Artificial light at night and cancer: Global study. Asian Pacific Journal of Cancer Prevention, 17(10), 4661–4664. https://doi.org/10.22034/APJCP.2016.17.10.4661
• Apoznański, G., Kokurewicz, T. S., & Petterson, S. (2021). Barbastelles in a production landscape: Where do they roost? Acta Chiropterologica, 23(1), 225–232. https://doi.org/10.3161/15081109ACC2021.23.1.019
• Barrientos, R., Vickers, W., & Longcore, T. (2023). Nearby night lighting, rather than sky glow, is associated with habitat selection by a top predator in human-dominated landscapes. Philosophical Transactions of the Royal Society B: Biological Sciences, 378(1883), 20220370. https://doi.org/10.1098/rstb.2022.0370
• Bowler, M., Beirne, C., & Tobler, M. (2020). LED flashlight technology facilitates wild meat extraction across the tropics. Frontiers in Ecology and the Environment, 18(9), 489–495. https://doi.org/10.1002/fee.2242
• Costello, E. C., & Colombelli-Négrel, D. (2023). Human activities at night negatively impact Little Penguin (Eudyptula minor) numbers and behaviours. Ibis, 165(3), 693–709. https://doi.org/10.1111/ibi.13217
• Deziel, N. C., Wang, R., & Warren, J. L. (2025). Perinatal exposures to ambient fine particulate matter and outdoor artificial light at night and risk of pediatric papillary thyroid cancer. Environmental Health Perspectives. Advance online publication. https://doi.org/10.1289/EHP14849
• Falchi, F., Cinzano, P., & Duriscoe, D. (2016). The new world atlas of artificial night sky brightness. Science Advances, 2(6), e1600377.
• Garratt, M. J., Jenkins, S. R., & Davies, T. W. (2019). Mapping the consequences of artificial light at night for intertidal ecosystems. Science of The Total Environment, 691, 760–768. https://doi.org/10.1016/j.scitotenv.2019.07.156
• Grubisic, M., Haim, A., & Bhusal, P. (2018). A transition to white LED increases ecological impacts of nocturnal illumination on aquatic primary producers in a lowland agricultural drainage ditch. Global Change Biology, 24(10), 4081–4089. https://doi.org/10.1111/gcb.14030
• Kim, A. Y., Velazquez, A., & Saavedra, B. (2024). Exposure to constant artificial light alters honey bee sleep rhythms and disrupts sleep. Scientific Reports, 14, Article 25865. https://doi.org/10.1038/s41598-024-73378-9
• Kyba, C. C. M., Kuester, T., & Sánchez de Miguel, A. (2017). Artificially lit surface of Earth at night increasing in radiance and extent. Science Advances, 3(11), e1701528. https://doi.org/10.1126/sciadv.1701528
• Lloyd, A., & Murray, J. (2022). The effects of light pollution on ocelots in Panama. Utah State University. Retrieved April 29, 2025, from https://www.usu.edu/biology/research/burs/spring-2022/light-pollution-ocelots
• Orlando, G., & Chamberlain, D. (2023). Tawny Owl Strix aluco distribution in the urban landscape: The effect of habitat, noise, and light pollution. Acta Ornithologica, 57(2). https://www.researchgate.net/publication/371590642
• Owens, A. C. S., & Lewis, S. M. (2018). The impact of artificial light at night on nocturnal insects: A review and synthesis. Ecology and Evolution, 8(22), 11337–11358. https://doi.org/10.1002/ece3.4557
• Sánchez-Pinzón, K., Reyna-Hurtado, R., & Meyer, N. F. V. (2020). Moon light and the activity patterns of Baird’s tapir in the Calakmul region, Southern México. Therya, 11(1), 115–122. https://doi.org/10.12933/therya-20-654
• Touzot, M., Voituron, Y., & Secondi, J. (2019). Artificial light at night disturbs the activity and energy allocation of the common toad during the breeding period. Conservation Physiology, 7(1), coz002. https://doi.org/10.1093/conphys/coz002