Let There Be dark

Let There Be dark

Light pollution harms the environment, wildlife, and even human health.

Image by Craig Mayhew and Robert Simmon, NASA GSFC

Civilization’s glare does more than interfere with stargazing; scientists have found that light pollution harms the environment, wildlife, and even human health.

For as long as humans have been able to tilt our heads back, we’ve been entranced by the night sky. We sailed vast seas using the stars as guides; planted and harvested according to the phases of the moon; built telescopes to probe our universe and beyond—stretching our understanding of who we are within this vast celestial fabric.

Then, in 1879, Thomas Edison debuted his electric lightbulb. Little by little, darkness has all but disappeared—and with it, our intimate connection to the night sky. Roughly two-thirds of the world’s population and 99 percent of those living in Europe and the continental United States now inhabit areas where the night sky measures above the threshold for light-polluted status.

Light pollution refers to sky glow, light trespass, glare, and overillumination. The celebrated glow of city lights often exceeds that of natural twilight—meaning the sky in urban areas never gets truly dark. Stars are invisible beyond the glare of streetlights, lit buildings, and flashing billboards.

“I worry that our lack of contact with the sky is doing something to us,” says science writer Ann Druyan in The City Dark, a documentary that explores light pollution. “Who knows what the ultimate effect will be?”

Researchers are asking this very question, and uncovering some troubling answers. Beyond disrupting astronomical research and the simple joy of stargazing, light pollution poses serious consequences for human and ecological health.

“Most people are not aware of the negative impact light at night has on our body function,” says University of Haifa Professor Abraham Haim, who studies the relationship between artificial-light exposure and health.

In June 2012, the American Medical Association adopted a policy acknowledging nighttime light as a health hazard. Excessive light at night—including that from computer screens and other electronic devices—disrupts sleep, particularly in young people. Light at night also inhibits the body’s production of crucial hormones, which may lead to weight gain and even cancer. The glare from unshielded lights also creates unsafe driving conditions.

Haim’s studies have found that people exposed to nighttime illumination are more susceptible to prostate and breast cancers. “[Light at night] harms production of melatonin, a hormone that is released from the pineal gland during the dark part of the twenty-four-hour cycle,” he says. “When this hormone is suppressed, the occurrence of cancer rises.”

Light pollution has widespread ecological ramifications as well. Animals’ mating, migration, sleep, and foraging behaviors are disrupted by unnatural increases in light. Nocturnal animals, such as bats, coyotes, deer, and moose, suffer from increased predation, lower reproductive rates, and impairment of night vision when their night ecosystem is compromised. Fireflies and glowworms are less visible to their mates in lighted environments.

Sea turtles are particularly vulnerable. Female turtles prefer nesting on dark beaches—a commodity that is increasingly hard to find. Baby sea turtles hatch from their nest at night, and instinctively crawl toward the brightest horizon, which used to be the ocean, glittering beneath the moon and stars. Now hatchlings are disoriented by the bright lights of beachfront resorts or roads and often crawl away from the ocean and into roads.

“It’s a major issue for seabirds,” says Fern Duvall, PhD, a wildlife biologist who regularly rescues downed birds in Hawaii—including some of the world’s rarest species. “Seabird chicks leave the nest at night,” he says. “They are attracted to lights and smack into them, or simply fly around them until they drop from exhaustion.”

The good news, though, is that unlike many causes of pollution, light leaves no residue and can be 100 percent reversed. By rethinking our approach to lighting, we can recover the magical dark skies of years past.

What you can do If You Have a Minute…

Flick the off switch. Light only what you need, when you need it. Turn off porch lights and flood lamps when you come indoors.

If You Have an Hour…

Talk with your neighbors or host an informal workshop about the impact of artificial light at night, and share ideas for reducing light pollution in your neighborhood.

If You Have a Month…

Work with your local government to push for outdoor lighting codes. The International Dark-Sky Association’s website,, has suggestions on how to reduce the impact of everything from sports lighting to historic lampposts.

If You Have $100…

Reduce your personal light footprint by changing your outdoor lighting, suggests Richard Wainscoat, of the Institute for Astronomy at the University of Hawaii. Look for shielded light fixtures that direct glare downward rather than up or to the side. Then swap out incandescent bulbs for low-pressure sodium lamps. They produce a limited color spectrum—low-level yellow wavelengths, rather than blue or white—which doesn’t attract insects and bats.

Join Us on the Journey

Sign Up

Enjoying this content?

Get this article and many more delivered straight to your inbox weekly.