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What Is Light Pollution?

Discover the human and environmental effects of light pollution


light pollution

This light pollution map shows the extent of nighttime lights across the United States.

International Dark-Sky Association

During the long history of life on earth -- for plants and animals as well as for humans -- the source of visibility at night was primarily celestial objects. Next in our evolutionary history came controlled firelight, which provided limited night illumination until the relatively recent development of electric lighting.

Today we've become so acclimated to artificial light we don't even think about its impact on people and wildlife. Granted, lighting is essential to our industrial society and the lifestyle to which even remote outposts of civilization have become accustomed. But light pollution -- an excess of artificial light in unwanted and/or unnecessary places -- has many downsides, and extensive night lighting has several well-documented adverse impacts worldwide.

Impacts of Light Pollution

  • Research shows our natural body clock and circadian rhythms (and, eventually, our health) are affected by lights at night.
  • Night lighting, like all uses of electrical energy, increases air pollution due to excess energy demands on power plants.
  • Birds, bats and other migratory wildlife use several clues in their (mostly) twice-yearly journeys, but starlight is a very important one, and extensive night glow is highly disruptive to the celestial clues these migrants rely upon to navigate.
  • Plant life is also seriously affected. As an example, many species of cacti bloom only at night and their pollinators are night-flying insects and bats. One especially beautiful cactus, the Queen of the Night, opens at night for only a few hours or so, and they simply can't reproduce with excessive light. And if these flowers are gone, so too are their plant-specific pollinators.
  • Scientists estimate that 1/3 of all human food is dependent on pollinators, and disrupting the food chain on a planet that evolved for millions of years with fixed day and night time periods could ultimately wreak havoc on our food supply and on us. See the National Academies Press' booklet "Resources on Pollinators."
  • Lighting that reflects upward not only illuminates the night sky and obscures our views of celestial bodies, but it's wasted energy. The International Dark-Sky Association estimates we waste 22,000 gigawatt hours a year up-lighting the night sky -- at 10 cents per kilowatt hour, that amounts to $2.2 billion annually. As a result of this light pollution, populated areas have lost the ability to see and experience the wonder of our stars, planets and astronomical events like meteor showers.

Lighting, Safety and Light Pollution

Safety is paramount in considering the benefits of night lighting. Can we be safe by lighting our way at night without bringing harm to ourselves and our ecosystems? Yes, we can. Here are just two examples:

  • Outdoor lights for roads, businesses and outside your home can have a simple shield placed on top, directing all beams downward.
  • Several cities, including Chicago, have adopted "Lights Out" programs whereby many tall buildings voluntarily turn off their office lights during migration, thereby minimizing the confusion and collision danger to which birds, bats, insects and other migrating animals are prone. This is to say nothing of the enormous energy savings and the increase in pollution that's avoided.

For an excellent resource on this entire problem I urge you to consult a book edited by Catherine Rich and Travis Longcore, Ecological Consequences of Artificial Night Lighting (Island Press). These light pollution issues have been extensively reported; the editors summarize the seriousness of the problem and, most importantly, the solutions, many of which we can all adopt.

This article was authored by Chicago-area conservationist Donnie Dann and appears here by permission.

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