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The Effects of Manmade Light on Nature

Insects being drawn to a porch light are an every-day demonstration of how manmade light at night disrupts natural biological cycles.

Working toward legislation to curb light pollution in Illinois.

Since the first living organisms appeared on our planet, the day/night cycle has provided the pulse to life on Earth. Vast numbers of species of plants and animals regulate key aspects of their life cycles by the regular changes from bright day to dark night. In comparison to the eons of time in which only the Sun, Moon and stars provided the light which governed the lives of most of Earth's organisms, the current period of our domination of the night with manmade light is just a momentary "experiment". Already, we are seeing the adverse results.

While we may think of night as a time for sleep, in the natural world, night is a time filled with activity. While some nocturnal creatures seem to be able to adapt to having manmade light fill their nights, others, like the insects trapped by the artificial glow of the light in the illustration above, have their lives totally disrupted by our lights. And, just as in humans as described on our Key Issues > Health Concerns page, many other organisms regulate much of their physiological, biochemical and behavioral activity via circadian rhythms which are synchronized by the day/night cycle of light and dark; science is only beginning to catalog the real-world effects of disrupting those cycles in the natural world around us.^1,2,3

 
One nocturnal activity which manmade lighting has been shown to disrupt is migration; this effect is frequently seen in night-flying birds. Nocturnal migrators (in the air, on the earth, or in the water) commonly navigate using the faint light of the stars or the Moon as guides; the unnatural glow from manmade sources, whether they're individual lights, bright buildings, or entire towns or cities, can overwhelm a creature's senses, and send it off course. If the migrator doesn't get to where it was heading, it will not complete the natural cycle, whether the destination was a place to feed, spend a season, or reproduce.^4,5

The dark of night serves as more than just a time for activity in the natural world. The changing length of day and night through the seasons serve as a trigger for important actions for many organisms, including budding, flowering and fruiting in plants, and mating, migration and hibernation in animals.^6,7 Artificial lighting at night can confuse an organism's sense of day and night, and disrupt its seasonal "clock"; that natural timing mechanism which has always served its species can be turned off by our careless filling of the night with our light.

 
Whether it is the flowering of a fruit tree, or the mating of the insects which pollinate it; the migration of a butterfly or a songbird; the disruption of the nocturnal feeding of bats or the reproduction of fireflies or frogs: artificial light in the wrong places has definite, harmful effects on the natural world around us. That same light, spreading from unfortunately all-too-common wasteful lighting installations, also represents the wasteful consumption of huge amounts of electricity (as described on our Key Issues > Energy page). The generation of that electricity creates its own, massive load on our environment.
 

Additional Resources:

  The article Fireflies and Lightbulbs: Does Manmade Light Impact Ecosystems? on this website delves into these issues in greater depth.  

There are many articles and studies availble on the Internet about manmade light and nature. Below, we give links to some which we find to be well-written synopses of some of the topics touched upon on this page; you will find many more on the Resources> Links page of this website.

¹ An April, 2002 article from Science News about ecology and manmade light.     ² A National Geographic 2003 article about manmade light and wildlife.     ³A study on artificial light and bats, 2000.     ⁴"A Silent Cry for Dark Skies", a 2008 article about manmade light and migration.     ⁵the Fatal Light Awareness Program, dealing with lighting's threat to migrating birds.     ⁶Wikipedia's article on photoperiodism.     ⁷ Another introductory article about photoperiodism.    

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