Light pollution’s insidious effects

Lighting the night harms humans, animals and plants

Posted 10/18/23

IN THE FORMERLY DARK —  Looking up on a clear night can be both humbling and awe-inspiring. The span of sable punctuated by distant points of light makes us feel small and also connected …

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Light pollution’s insidious effects

Lighting the night harms humans, animals and plants


IN THE FORMERLY DARK —  Looking up on a clear night can be both humbling and awe-inspiring. The span of sable punctuated by distant points of light makes us feel small and also connected to the greater universe. 

This view is under threat from a familiar adversary: humanity. Artificial light is making it harder for more and more people to experience nighttime the way our ancestors did. Not only is light pollution a threat to star gazing, but it has an effect on our health and the environment.

It is estimated that 83 percent of people live under a measurable level of skyglow, the term used for light-polluted skies, and 23 percent of the earth’s landmass is affected. Maps of light-polluted regions show dense areas of light around urban sites, light that stretches far beyond the city limits.

Not only is the current level of light pollution affecting the vast majority of people, but it is also increasing. According to Scientific American, between 2011 and 2022 researchers found that globally, light pollution increased by 9.6 percent a year. 

Based on these results, if there are 250 visible stars in the sky when someone is born, by the time they’re 18 they’ll see only 100, and over that same period the sky will have increased in brightness by more than a factor of four. reports that in North America, light pollution is growing at 10.4 percent per year, compared to 6.5 percent in Europe.

This may seem like a negligible loss; after all, being able to see the stars isn’t vital. However, darkness is hugely important to overall health. National Geographic reports that an increased amount of light at night lowers melatonin production, which results in sleep deprivation, fatigue, headaches, stress, anxiety and other health problems such as obesity and diabetes. 

Recent studies also show a connection between reduced melatonin levels and cancer. 

Having times of set darkness and light stabilizes and supports our circadian rhythms, helping to regulate mood and growth and improve cognitive abilities and reaction times.

It harms the environment too

Light pollution is damaging to our natural world as well. In his paper, titled “Missing the Dark: Health Effects of Light Pollution,” Ron Chepesiuk details some of the effects light pollution is having on our environment.

Approximately 200 species of migratory birds make their flights over North America at night, and the reflection of light on tall buildings confuses them, especially in bad weather. Many of the birds collide with the windows and die as a result. Estimates of these collision deaths across North America approach one billion birds.

Famously, sea turtle hatchlings use the light of the moon to navigate their way down the beach into the sea. Artificial lights disorient the hatchlings, causing them to move toward the bright lamp rather than the moon’s reflection on the water.

The impact extends beyond birds and sea turtles. Plants need times of darkness and light in order to grow properly and respond to the seasons. Frogs have been shown to inhibit their mating calls when exposed to excessive light, reducing their capacity. Bats are not able to feed as effectively. Moth populations have declined due to artificial lights. Thirty percent of vertebrates and 60 percent of invertebrates are entirely nocturnal, and light pollution is effectively causing habitat loss for these animals.

Dark Sky certification is the premier international organization combatting light pollution. Communities around the world are coming together to demand better quality lighting to protect and restore natural darkness by seeking Dark Sky certification. There are more than 200 International Dark Sky Places and at least as many places are working toward certification. 

This independent certification program recognizes best practices in lighting, including adopting quality lighting policies, retrofitting existing lights, monitoring sky quality, and providing opportunities for people to enjoy the nocturnal environment. 

What can we do?

The simplest thing individuals can do to combat light pollution is to ensure that outdoor lights are turned off when not in use. It is also important to close blinds at night to block indoor light from escaping into the outdoor environment.

Save our Stars advocates for a switch to amber-colored LED lights that do not emit the blue part of the light spectrum. This means that the light does not travel as far and that the light is more diffused. The group also recommends a full shield that directs the light downward, where it is most useful, rather than exposed or partially shielded lights that waste light by sending it up and out. The light should also be no brighter than absolutely necessary, and turned off when not needed with timers and motion sensors. For more, visit

If you’re moved to be a part of teams of people who measure light pollution by finding constellations and reporting on them, the Globe at Night program might be of interest. Globe at Night is an international citizen-science campaign to raise public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations from a computer or smartphone. The organization has collected more than 200,000 measurements from people in 180 countries over the last 14 years. For more, visit

light pollution, globe at night


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