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A mountain lion at night, with the city lights of Los Angeles in the background.
This uncollared adult female mountain lion was photographed with a motion sensor camera in the Verdugo Mountains in August 2016. Los Angeles city lights in the background. Photo Credit: National Park Service

For billions of years, all life has relied on Earth’s predictable rhythm of day and night. It’s encoded in the DNA of all plants and animals. Humans have radically disrupted this cycle by lighting up the night.

Plants and animals depend on Earth’s daily cycle of light and dark to govern life-sustaining behaviors such as reproduction, nourishment, sleep, and protection from predators.

Scientific evidence suggests that artificial light at night has negative and deadly effects on many creatures, including amphibians, birds, mammals, insects, and plants.

Artificial lights disrupt the world’s ecosystems

Nocturnal animals sleep during the day and are active at night. Light pollution radically alters their nighttime environment by turning night into day. According to research scientist Christopher Kyba, for nocturnal animals “the introduction of artificial light probably represents the most drastic change human beings have made to their environment.”

“Predators use light to hunt, and prey species use darkness as cover,” Kyba explains. “Near cities, cloudy skies are now hundreds or even thousands of times brighter than they were 200 years ago. We are only beginning to learn what a drastic effect this has had on nocturnal ecology.”

Glare from artificial lights can also impact wetland habitats that are home to amphibians such as frogs and toads, whose nighttime croaking is part of the breeding ritual. Artificial lights disrupt this nocturnal activity, interfering with reproduction and reducing populations.

“When we add light to the environment, that has the potential to disrupt habitat, just like running a bulldozer over the landscape can.”

– Chad Moore, formerly of the U.S. National Park Service

Artificial lights can lead baby sea turtles to their demise

A hatchling loggerhead sea turtle turns inland following human-made lights instead of seaward toward safety. (Photo credit: Blair Witherington)

Sea turtles live in the ocean but hatch at night on the beach. Hatchlings find the sea by detecting the bright horizon over the ocean. Artificial lights draw them away from the ocean. In Florida alone, millions of hatchlings die this way every year.

Artificial lights have devastating effects on many bird species

Migrating geese

Birds that migrate or hunt at night navigate by moonlight and starlight. Artificial light can cause them to wander off course and toward the dangerous nighttime landscapes of cities. Every year millions of birds die colliding with needlessly illuminated buildings and towers. Migratory birds depend on cues from properly timed seasonal schedules. Artificial lights can cause them to migrate too early or too late and miss ideal climate conditions for nesting, foraging, and other behaviors.

Ecosystems: Everything is connected

In addition to their ecological role, fireflies are a source of wonder and delight for children and adults.

Many insects are drawn to light, but artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination. Some predators exploit this attraction to their advantage, affecting food webs in unanticipated ways.

Get involved

Learn more about how light pollution impacts wildlife and ecosystems

Explore the Artificial Light at Night (ALAN) Database to find the latest scientific literature on how light pollution affects wildlife. There is no login required. Research on specific topics can be found by entering a key word (such as birds, turtles, or migration) into the search window in the upper right. Search results will then appear in the main part of the window.

Get involved

Protect the natural nighttime environment

Join DarkSky’s global network of advocates working to protect the night from light pollution! The process is simple: Take the DarkSky 101 training and you will be invited to join DarkSky’s global communication platform, get access to exclusive advocate resources, and be invited to join additional monthly advocate training on various aspects of light pollution and dark sky conservation.