This Green Life
A monthly journal of sorts by Sheryl Eisenberg

SEPTEMBER 2012 (links updated 2014): Light pollution can be harmful to life and fatal to migrating birds. It also kills one of nature's great spectacles—a starry sky. You can help reduce it.

Restore the Night Sky
Do your lighting right

If you have never seen the Milky Way, you're not alone. Neither have most Americans.

I've had the luck to experience it on camp-outs and travels, though never where I have lived. The first time was a eureka moment. I discovered the galaxy does look like a splash of milk.

The "milk" is the blur of thousands of stars, which are visible to the naked eye when the sky is dark enough.

Before the modern era, the sky was always dark enough. Now, in much of the world, it never is. We can thank artificial lighting and urbanization for that.

The result is a case of myopia writ large. We can no longer see our home galaxy.

The word galaxy, by the way, means milk in the original Greek. To the ancient Greeks, who observed the Milky Way without telescopes, the milky streak was a mystery. Poets and philosophers that they were, they came up with varied explanations, both mythic and scientific, one of which turned out to be right. Had they lived with light pollution like ours, they wouldn't have had a clue.

Today's light pollution is so bad in places that even modern astronomy with all its seeing aids is at risk.

So is wildlife.

Light is one of the environmental cues that tell animals where to go. Newly hatched sea turtles are drawn to the brightest point on the horizon, which, in a state of nature, would be the moonlit sea. Add artificial lights to the environmental mix and they may run to the mall instead.

By contrast, female sea turtles with eggs to lay avoid the light. If the beach is too bright, they will not dig their nests. Studies have shown that in the presence of artificial lights, salamanders lie low for an extra hour after dusk before coming out to hunt and male tree frogs fail to call for mates at breeding time.

Birds who migrate by night, navigating by the moon and stars, are confused by big city lights. Lured downtown by the shimmering buildings, they circle endlessly, collide with the towers and die in vast numbers every spring and fall. Moths, too, die in droves when attracted by artificial lights, as every schoolchild knows.

Other effects of light pollution stem from disruption of circadian rhythms, not only in animals but plants. Nighttime lighting can impair a plant's ability to generate phytochrome. Abnormal levels of this photosensitive hormone can have consequences for a plant's flowering cycle, seed germination and dormancy.

Humans are not immune either. Exposure to excessive light at night reduces production of our own photosensitive hormone, melatonin, and has been linked to breast cancer.

Research into the health and environmental effects of light pollution is still in its infancy, but we already know enough to know we have to bring light pollution down. We also know how to do it.

The solution does not involve curtailing nightlife, hampering the nighttime economy or compromising safety. It just requires directing lights where they're needed and eliminating waste.

While you're waiting for local governments and corporations to get on board, you can get started at home. Here's how:

1) Only turn on outdoor lights when needed—or install motion sensors.

2) Point the lights downward and outfit them with "shields" to prevent light from traveling sideways. The goal is to shine them only where illumination is wanted—not in people's eyes or on other people's property (a case of "light trespass").

3) Lower the wattage of your bulbs and put them on dimmers. Bright lights and dark shadows don't improve safety, but reduce it.

4) Close curtains at night to keep indoor light in. If you live in a multi-story building, use black-out curtains to prevent bird crashes.

And, of course, please use energy-efficient lights to cut global warming emissions even more than you'll be doing already.

If all this talk about the night sky has sparked an interest in exploring the heavens, look up your local amateur astronomers club. A dark sky teeming with stars is one of nature's great wonders.

—Sheryl Eisenberg

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Fantasy cityscape with starlit sky


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On This Topic

OUR LIGHTS LEAD BIRDS ASTRAY during migration, contributing to 100 million deaths a year in the U.S. and Canada from collisions with buildings. Watch this video by the Fatal Light Awareness Program (FLAP) to learn more.

Lights at entrance to the Holland Tunnel, New York City
THE STARS ARE VERY FEW IN NEW YORK on the best of nights. Even the moon can get lost amid the throngs of electric lights when it hangs low in the sky. (In this photo, taken on Canal Street, it is the second bright light from the left.)

Light pollution from space
LIGHT POLLUTION IS WORST in urban and suburban areas, where three-quarters of Americans live, but affects outlying places as well. At Dante's View in Death Valley, the lights of Las Vegas, 85 miles away, are brighter than the planet Venus on a clear night.

See the world light map from which the image above was excerpted at This Green Blog.

Image Source: NASA via Visible Earth.


One-fifth of Us Have Lost Sight of Milky Way

The New Yorker
The Dark Side: Making War on Light Pollution

The New York Times
Stargazers Seeking Clearer Skies

National Geographic News
Light Pollution Taking Toll on Wildlife
Light Pollution Raises Risks of Breast Cancer

International Dark-Sky Association
Practical Light Pollution Guides

Starry Night Lights
Night Sky Friendly Outdoor Lighting

More to Do

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Sheryl Eisenberg is a writer, web developer and long-time advisor to NRDC. With her firm, Mixit Productions (, she brought NRDC online in 1996, designed NRDC's first websites, and continues to develop special web features for NRDC. She created and, for several years, wrote the Union of Concerned Scientists' green living column, Greentips, and has designed and contributed content to many nonprofit sites. Sheryl makes her home in Tribeca (NYC), where—along with her children, Sophie and Gabe, and husband, Peter—she tries to put her environmental principles into practice. No fooling.
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