Why a Dark Sky Matters

Night lights create a dazzling aerial view, but 24/7 lighting harms ecosystems and human health.


Night lights create a dazzling aerial view, but 24/7 lighting harms ecosystems and human health.
Night lights create a dazzling aerial view, but 24/7 lighting harms ecosystems and human health.

For those living in remote areas, seeing the stars is no big deal. But for the many people who live in cities, spotting the Big Dipper can be tough. City lights are to blame — everything from streetlights to stadium lights to garage lights. And it turns out these lights mess up a whole lot more than just our view of the galaxy.

“I remember growing up seeing stars all the time, and now I don't see 'em. There's so much light pollution from houses,” said Beth Bedford, a nature enthusiast from Willoughby, Ohio. “Auto dealers are the worst. When you just wanna go out in the summer and enjoy the summer nights and you've got all this light and there's no way to see the stars or anything and to enjoy it.”

Bedford isn’t alone in lamenting the loss of the night sky. I met her at a recently opened “dark sky park” in Geauga County, Ohio. It’s one of 12 parks certified by the International Dark Sky Association. Park naturalist Chris Mentrek said all of them create an oasis of dark.

“We're 32 miles from the Public Square hotdog cart, but it's already a whole different world when we look over the sky because it's just intensely dark out here,” said Mentrek.

Dark sky parks, with their star-filled nights and open fields, make great locations for observatories.
This monitor sits atop a green roof at Ohio's Observatory Park and tracks how dark the sky is.  It's part of a worldwide science project that monitors light pollution.

This allows for prime stargazing. But Mentrek said that’s not the only benefit of having the lights switched off.


“So it's not just that it, you know, wrecks our view of the cool stuff that we astronomers wanna study, like stars and faraway galaxies, but it can also start to kind of mess with these rhythms that nature's adapted itself to,” he said.

Mentrek explained that light pollution affects the health of the ecosystem and the animals living in it, including people. By turning on artificial lights 24 hours a day, people start to disrupt natural circadian rhythms of lightness and darkness that human bodies expect, he said.

“And so, then hormone levels in your brain can slowly come a bit out of the balance that they were adapted to. And you can start to see human health effects,” he said. “And then, of course, there's all the other animals who are accustomed to a nice, dark night and then all of a sudden we've brought in these strange artificial lighting sources. So it can be a little bit disorienting.”

Many animals depend upon clear, starry nights for navigation. Light pollution draws birds and fish off course; bats get confused; sea turtles looking for the light of the moon end up following rays from street lamps onto highways; even the South African dung beetle, which rolls its dung ball back home with help from the Milky Way, runs askew without stars.

“So if there's all these artificial lights, the poor little guys can't find their way, and they're just kind of wandering around aimlessly,” Mentrek said.

Dung beetles need the stars to navigate as they roll their smelly treasures homeward.
Dung beetles need the stars to navigate as they roll their smelly treasures homeward.

On top of that, light pollution disrupts the ability of nocturnal creatures to mate, migrate, feed, and pollinate. Species that rely on the safety of darkness to forage, for instance, will delay doing so in the glare of streetlights for fear of getting eaten themselves. Scientists are still learning how and why light pollution disrupts so many species, but there seems to be no question that behavior is being altered.

In humans, too much bright light creates hormonal havoc. It messes with the body’s production of melatonin. The World Health Organization calls shift work a probable carcinogen, and researchers are finding more and more evidence linking light to everything from obesity to mood disorders to heart disease.

That’s why many environmental and public health advocates are making a concerted effort to change the way we light our world. Travis Longcore, a professor at the University of Southern California who studies the effects of light pollution on the natural world, said there are five main things people can do to limit light pollution without compromising safety or other concerns.

First off, said Longcore, determine if a light is truly needed for the area. If a light is necessary, consider whether the area could be lit with a lower-intensity bulb.

Another thing to consider is direction. Shield the light so it illuminates just what you need, like a sidewalk, and avoid what Longcore calls the “quintessential barn light.” “It's just a big glare bomb,” he said.

Next on his checklist is duration. Don’t keep a light on 24/7 if it doesn’t need to be. France recently mandated shops turn off their lights after 1 a.m., and the country expects to save two million euros in energy costs and cut over 200,000 tons of CO2 emissions per year.

The colors we see are functions of wavelengths of light.
The colors we see are functions of wavelengths of light.

His last tip is color: avoid bright white. It contains a mixture of all the colors on the visible spectrum. Dim red light is best for nighttime because it has longer wavelengths with the least power to mess with circadian rhythms and affect melatonin. He said many stores sell yellow “bug lights” that would be good night lighting for humans and the environment.

At Ohio’s Observatory Park, for instance, the pathways are lit up by miniature street lamps that face down and glow red. Longcore said parks like this can drive change.


“What you love to see around a dark sky park is that people recognize the benefits this brings to the community,” he said. “As long as people are aware that there are many reasons that people are concerned about and want to see smart night lighting — that range from health to wildlife to stars — it can set up a local culture of respect for those issues and sets of behaviors that go along with it.”