For almost all human history, the night sky brimmed with stars—leading us to reflect on our place in the Universe and inspiring science, philosophy, art and literature. But excessive artificial light is rapidly obscuring our starry nights, with repercussions far beyond depriving us of stargazing.
Studies show that light pollution can increase risks for obesity, sleep disorders, depression and diabetes. Moreover, as much as half of outdoor lighting is wasted because it is poorly aimed or unshielded, which increases emissions that contribute to climate change.
When it comes to wildlife, the effects on everything from insects to night-prowling predators can be severe.
Birds that migrate or hunt at night use the moon and stars to navigate. Artificial light can lead them off course toward dangerous city landscapes. Every year millions of birds die in collisions with illuminated buildings.
Many insects—vital food sources and pollinators—are drawn to light and die flying into lamps or collapse after circling for hours. One study suggests that light could wipe out some 60 billion insects in a single summer.
Bats will change flight routes between roosting and feeding sites to avoid light and predators. This can waste energy and cause stress, which can affect reproduction.
Night light also confuses sea turtle hatchlings. To get to sea, they rely on moonlight. Light from hotels and homes can draw them inland instead, where they can get stranded or squashed on roadways. Glare also disrupts frogs and toads, which use nighttime croaking in their breeding rituals. Even fish are affected. When street lamps or porch lights shine into waterways, it can change their behavior.
Juvenile chinook salmon, for example, will gravitate toward a river’s surface and linger, becoming easy prey. With dams already impeding salmon spawning, this predation ultimately affects the population of undernourished, imperiled orcas in the Salish Sea that rely almost exclusively on a chinook diet.
The good news is light pollution is reversible. Some cities are now incorporating street lighting that shines down rather than up and asking that night lighting in office buildings be reduced or eliminated. “There’s a natural connection between dark skies and wildlife conservation,” says Defenders’ Erica Prather. “A dark sky is a precious resource for all life on Earth.”
Dark Sky Dos
Practice lights out from 11 p.m. to 6 a.m.
Flip off lights when heading home from an office building.
Shine outdoor lighting down rather than up, light only what is needed and use dimmers, motion sensors and timers.
Change outdoor bulbs to warmer hues, like amber and yellow.
Start a local initiative to ensure lights on billboards face down.