Shedding light on the importance of darkness to nature

  • This great horned owl sits perched in the black of night on the branch of a walnut tree in winter during a snowfall.

    This great horned owl sits perched in the black of night on the branch of a walnut tree in winter during a snowfall. Getty Images/iStockphoto

  • Luna moths, a giant silk moth named after the Roman moon goddess, has pale and luminous green wings.

    Luna moths, a giant silk moth named after the Roman moon goddess, has pale and luminous green wings. Courtesy of Deborah Davis

Posted12/17/2018 6:00 AM

"Boy, it's dark!" I mutter at 4:30 p.m. when I leave the nature center. My husband winks as he reminds me that this happens every December and that I say exactly the same thing each year. He predicts, correctly that, come June, I'll exclaim, "Look! It's still light out!" at 8:45 p.m.

Changes in day length seem gradual to us Earthlings as our planet takes its annual spin around the sun.


Down here, the daily subtleties of changing light are easy to miss. When it starts to get dark in the evening, the streetlights go on.

If it's still dark when we get up in the morning, we turn on lights.

The distinction between night and day is barely noticeable when you've got light switches.

so with wildlife. The light/dark cycle is one of the most important influences on the biological world. It's also the most constant and predictable.

You can set your watch -- or your calendar -- by the natural light cycle. Animals and plants, in fact, do.

This is what cues flowering time, pollination, fruit-set, and reproduction. It affects feeding, courtship, and movement. It's a factor in metamorphosis and migration.

In other words, the biological world needs daylight and, just as importantly, it needs darkness.

Here's where the challenge lies. Darkness is disappearing.

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The 130 years since Thomas Edison devised the incandescent light bulb are but a fraction of time in the history of life on earth.

In this short period, artificial light has spread across continents, illuminated shorelines and penetrated the oceans. Ecological darkness has been interrupted, and in some cases, it has disappeared.

To be sure, we humans greatly benefit from artificial lights. A growing body of research is shedding light on the ecological repercussions of illuminating the world.

Nocturnal wildlife and plants are impacted in ways we don't fully understand yet.

We do know that the intricate relationships of predator and prey, pollinator and plant are disrupted by artificial light.

Lights throw migration out of sync, and that in turn impacts feeding patterns. Artificial light affects metamorphosis in amphibians and disorients nesting reptiles.

The glow of fireflies is a natural light in the darkness.
The glow of fireflies is a natural light in the darkness. - John Starks | Staff Photographer

A close-to-home example is fireflies. Who doesn't love fireflies? Lots of people have fond childhood memories of catching fireflies on summer evenings, and marveling at the magic they create in fields and forest. Of course, the blinking lights are not magic. The lights are the firefly's way of attracting a mate.

The patterns of flashes in the dark send species-specific messages that are critical in courtship and reproduction.

If you've seen fewer fireflies in recent summers, look to see how many yards are lit up in your neighborhood.

Parking lot lights by fields and bright LED signs along roadways also reduce the darkness that fireflies need. No darkness, no flashing, no love life, no fireflies next summer.

But fireflies are just for fun. We could do without them, you may say.

How about pollinators? Many of the plants in your garden and crops in the field are pollinated in the dark of night by moths.

Moths are drawn to your porch light, to streetlights and parking lots. As you know at home, they never seem to wise up and figure out what the light is -- and this means they're spending precious time bashing into your screen instead of pollinating the plants in your garden.

A bit farther afield, scientists have studied the effect of artificial light on zooplankton in the arctic zone. They found that even slight changes in ambient light alter the planktons' cyclical movement in the ocean.

You may not feel much kinship with minuscule aquatic creatures in the Arctic, but consider the bigger picture. "Zooplankton play an important role in the sequestration of carbon dioxide, carrying millions of tons of carbon vertically in the ocean during their daily cyclical movements," according to a recently published report (

"It is clear that artificial light affects zooplankton, which ripples through the ecosystems of the ocean. This then affects the atmosphere above the surface of the water." Amazing how everything connects.

"Well, I use LED lights," people say, believing that they're doing something good for the environment.

LEDs are not the saviors that you may think they are.

Ironically, with the immense popularity of "energy-saving" LEDs, people are using more lights than ever.

Compounding the problem is the harmful effect of blue-spectrum LED lights. These are the ubiquitous white-ish lights that are blindingly bright. They influence melatonin levels in humans (affecting our sleep patterns), and they disorient migrating wildlife such as turtles and birds.

Researchers are trying to keep up with the rapid growth in the use of the blue-spectrum LEDs. So far, they give LEDs an emphatic thumbs-down.

So, wildlife and plants are once again taking a hit from humans.

But there's good news in this dark story. The loss of night does not have to be permanent. Light pollution is a completely solvable problem. Reducing our use of outside lights is easy, painless, and economical.

Consider how much light you really need. Maybe instead of two porch lights, one will do. You can put outside lights on a timer or a motion-detector instead of shining all night.

If you're concerned about safety and feel you need outdoor lighting, be sure to direct the lights downward. Use fixtures that shield the light from the sky. Select warmer-spectrum LED lights for minimum impact.

The Illinois Dark Sky Association has excellent guides for purchasing and installing wildlife-friendly lights at

Friday, Dec. 21, will be the winter solstice, the longest night of the year. Step outside at dusk and watch as darkness falls. Listen for the shuffle of raccoons in the alley and the yipping of coyotes by the creek. Imagine the fireflies overwintering under the fallen log out back.

Know that nighttime is good -- for them, and for us.

Turn the lights off for the solstice, and give the gift of darkness to the world.

An owl out there is winking at you.

• Valerie Blaine is the Environmental Education Manager for the Forest Preserve District of Kane County. You may reach her at


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