In defense of dark skies: How artificial lighting disrupts natural cycles

Darkness is a tough sell, especially on the winter solstice, the longest night of the year. But a dark night sky is a good thing. Ask an owl, or a firefly, or a wise man following a star.

What's so good about the dark? Natural darkness is just as important as natural light. Plants and animals evolved with light-dark cycles, and these cycles affect our health and well-being.

The light-dark cycles create a natural rhythm in our days and night. This is circadian rhythm, also called our biological clock. Sleep, mood, eating, and exercise are all part of the rhythm. We've got the rhythm, and all life-forms swing to beat.

Since the advent of electricity, circadian rhythm has been increasingly disrupted. Artificial lighting has launched us on a campaign to conquer darkness, and we're darn near successful. We light streets, parking lots, billboards, beaches, buildings, stadiums, statues, flagpoles, houses, trees … you name it. The tools at our disposal are mercury vapor, metal halide, and fluorescent lights. LED technology has revolutionized the lighting industry, allowing us to illuminate more, cheaper, and brighter.

All this round-the-clock lighting has thrown us out of sync from the natural rhythms of our evolutionary history. Not only are we out of sync, but we're affecting the life cycles of other animals and plants as well.

Take plants, for example. Most of us know that if a house plant doesn't get enough daylight, it won't grow well. Similarly, if it's in constant light, it may not flower or produce fruit. Trees growing under streetlights that glow from dawn to dusk never get a dark cycle. They respond in a variety of ways. Some species, such as birches, catalpas, and elms, are highly sensitive to artificial light. Their dormancy and flowering times are altered by continual light. Streetlights cause some leaves to keep pores (or, stomata) open longer than normal, which makes them more susceptible to air pollution and water stress.

Night lighting affects entire food webs. Insects swarming around streetlights on a summer night are a good example. If moths spend hours in kamikaze flights around porch lights, they are not pollinating the plants in your garden. If bats spend more time feasting on the insects by the lights, they are not eating insects in the marsh. Take fireflies, another good example of a nocturnal insect. When artificial lights illuminate lawns and fields, female fireflies find it harder to read the courtship signals of flashing males. Their trysts must take place in the dark. Fewer fireflies, fewer spiders that prey on fireflies. Fewer fireflies, more of the insect prey they would have eaten. And way less fun for kids on summer evenings.

The complexity of the effects of light pollution is well documented in publications such as "Ecological Consequences of Artificial Night Lighting." There is growing evidence that artificial light affects the behavior, feeding, and breeding cycles of all types of wildlife, including reptiles, fish, birds, mammals and insects.

And the problem isn't limited to cities - it extends to rural areas, too. As the book's editor Catherine Rich wrote, "As we light up the night with ever more powerful lights … we are wreaking havoc on creatures with physiologies far more delicate than ours, interfering with the lifeways of suites of organisms that have evolved over millennia with a dependable pattern of light and dark."

What about us? Modern lighting is hailed as a way to extend our days, allowing us to work and play and sell and purchase around the clock. We can do anything, anywhere, anytime. The people who walked in the darkness now run around like crazy in the light. This is a good thing, right?

There are benefits, to be sure. I, for one, am glad that hospitals are open 24/7 with well-lit operating rooms. There is no doubt that technology has improved our lives, but the profligate illumination of the planet has cost us in ways we're only now beginning to see.

Our dissociation from natural light takes a physiological toll. There's only so much activity we can do in 24 hours. Sleep, that restorative, restful dreamtime, is a casualty of artificial light, and insomnia a modern plague. Clark Strand examined the topic in his book "Waking Up to the Dark: Ancient Wisdom for a Sleepless Age."

"In centuries past," Strand wrote, "the hours of darkness were a time when no productive work could be done. … People took to their beds at nightfall, but not merely to sleep. They touched one another, told stories and, with so much night to work with, woke in the middle of it to a darkness so luxurious it teased visions from the mind and divine visitations that helped to guide their course through life."

Roger Ekirch is another author who has reflected on the importance of dark nights. True night time is gradually being eliminated, Ekirch wrote in his book, "At Day's Close: A History of Nighttime." Our collective dreams and visions suffer for the lack of nighttime. We need the darkness of night, he opined, for "a better understanding of our inner selves."

There's another element to all this. It's called beauty. A dark, star-filled sky is just plain beautiful. It's awe-inspiring, glorious and utterly magnificent. It puts us in our place in the vast universe, making us humble and rich in spirit at the same time.

The winter solstice is a time to welcome the natural return of the sun. Let's embrace the natural darkness as well. Just think, no matter how wise those Magi were, they couldn't have seen the star without a dark night sky.

• Valerie Blaine is the Nature Programs Manager for the Forest Preserve District of Kane County. You can reach her at

"A dark, star-filled sky is just plain beautiful," says naturalist Valerie Blaine. Courtesy of Thinkstock by Getty Images
The Orion constellation can be spotted in a dark night sky. Courtesy of Thinkstock by Getty Images
A satellite image taken in October shows light pollution in heavily-populated areas of the planet. Courtesy of NASA
In areas with lower light pollution, stars can be more clearly seen in the night sky. Associated Press

Keeping night skies dark: What you can do

Reconsider the need for outdoor lighting. If lighting is essential:

• Select the correct location and intensity of artificial light

• Use light fixtures that direct light only where needed - toward the ground for pedestrians or traffic

• Do not direct lights skyward, up into trees, or horizontally

• Turn off or dim lights during spring and fall bird migration

• Keep indoor light in, by using curtains or shades

• When planting trees in areas with artificial, continuous lighting, select species with low sensitivity to light (see <a href=""></a>)

• Step outside at night and enjoy the starry sky

<b>Learn more</b>For more information, check out these websites:

• International Dark Sky Organization, <a href=""></a>

• Globe at Night, <a href=""></a>

• Natural Resources Defense Council, <a href=""></a>

• National Geographic, <a href=""></a>

• Purdue Extension Office, <a href=""></a>

- Valerie Blaine

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