Artificial lighting at night can negatively affect humans, plants, and animals as well as hinder our view of the night sky. Astronomers define this light pollution as “artificial light that shines where it is neither wanted, nor needed.” The International Dark Sky Association (IDA) describes it as the “inappropriate or excessive use of artificial light,” of which sources include exterior and interior lighting, advertising billboards and signage, commercial properties, sports stadiums, streetlights, and the like. With advancements in technology, common artificial light sources have come to include computer monitors, smart phones, tablets, television, and gaming screens.
Thomas Edison’s electric lightbulb first lit a street in New York in 1882, and there’s no arguing how helpful that invention has been to mankind. It’s difficult to imagine life without the benefits of artificial light extending our days to work or play, lighting our way safely home, and enhancing the functionality of our living spaces.
But scientific research is gradually gathering evidence regarding the dangers of light pollution. Almost 150 years after the modern era of lighting began, our fervor for light may simply be too much of a good thing.
Health Hazards for Humans
Before artificial light was developed, people lived for centuries with a light/dark cycle that depended on the sun. That 24-hour cycle, known as the circadian clock, is deeply embedded in human biology and is affected by light and darkness. Although the health effects of light pollution have not been studied in humans as extensively as in wildlife, there is increasing evidence to indicate a consistent association between exposure to artificial nighttime light and health problems.
An article by Bob Parks in Sky & Telescope explained that disruption of the circadian rhythm has been linked to sleep disorders, depression, hypertension, attention deficit disorder, obesity, diabetes, and heart disease. The problem, at least in part, is that disruption of the circadian cycle lowers levels of melatonin, which regulates several biologic activities including metabolism and immune responses and is a strong antioxidant and anti-carcinogen. Lowered melatonin levels have been correlated to a higher chance of developing breast, colorectal, and prostate cancers.
For those who consistently work nights, the circadian clock can adjust and regulate the body normally if light/dark patterns are controlled. For those who work rotating shifts, it is more difficult. Studies in such journals as Cancer Causes and Control, the Journal of the National Cancer Institute, and Epidemiology have studied female employees working a rotating night shift and found that an elevated breast cancer risk is associated with occupational exposure to artificial light at night. While the research on the shift work/cancer relationship is not conclusive, the International Agency for Research on Cancer classified shift work as a probable human carcinogen in 2007.
Effects on Ecosystems
The regular rhythm of night and day provides plants and animals indicators for their cycles of feeding, mating, and migrating. Light pollution alters this natural rhythm and impacts can be seen in almost every ecosystem.
Extended exposure to artificial light inhibits many trees from adjusting to seasonal variations, according to Ecological Consequences of Artificial Night Lighting by Winslow Briggs. This results in consequences for the animals that rely on trees for habitat. Research on many species shows that light pollution is detrimental in both urban and rural areas.
"Light pollution can disorient new sea turtle hatchlings such that they are drawn away from the sea, increasing the risk they will die before reaching the water."
For instance, light pollution can affect fish by suppressing melatonin and disrupting reproduction and growth. It dramatically affects the nesting behavior of adult sea turtles and disorients new hatchlings such that they are drawn away from the sea, increasing the risk they will die before reaching the water. Some species of bats associate artificial light with predators, meaning in brightly-lit cities they attempt to alter their feeding patterns but are left with nowhere to go. Researchers in the Red Sea also found that light pollution acts as a chronic disturbance that may impact the future of coral reefs. Frogs have been found to inhibit their mating calls when they are exposed to excessive light at night and the list goes on to primates, marsupials, rodents, and insects.
Behavior of birds is particularly disrupted by light pollution. Hundreds of species of birds fly their migration patterns at night and, especially when there is low cloud cover, they become confused by brightly lit buildings, communication towers, and other illuminated structures. Michael Mesure, executive director of the Toronto-based Fatal Light Awareness Program, explains that birds are attracted to light, which in turn causes many to have fatal collisions with structures.
"About 10,000 migratory birds are injured or killed annually by crashing into New York City’s high-rise buildings."
According to Glenn Phillips, executive director of the New York City Audubon Society, about 10,000 migratory birds are injured or killed annually by crashing into the city’s high-rise buildings. The annual estimates of birds dying from collisions across North America range from 98 million to close to a billion and the U.S. Fish and Wildlife Service estimates five million to 50 million birds die each year just from collisions with communication towers.
Reclaiming the Dark
Clearly, reducing use of lights will reduce light pollution. Even in a world that operates 24/7, many locales are finding ways to turn down the glare. Research continues and ideas are being implemented around the globe as the impacts of light pollution on humans and animals becomes more of a mainstream concern.
For example, a two-decade study by biologists studying how light pollution from a building in Chicago affected birds found that turning off interior lights at night had a dramatic effect. Halving the number of windows illuminated at night decreased bird collisions and cut bird deaths by an estimated 60%. Many cities have now adopted a “Lights Out” program to turn off building lights during bird migration.
The IDA works with towns and cities that commit to lessening light pollution through measures such as shielding lights to point downward, adding timers, and avoiding the blue-white light spectrum, which has a greater adverse impact on wildlife. The association outlines the following five principles for responsible outdoor lighting:
In the United States, Flagstaff, Arizona, was the world's first international dark sky place, receiving the IDA designation 2001. Home to two observatories, Flagstaff has been a forerunner in proving that economic development can progress without light pollution. At least nineteen U.S. states, the District of Columbia, and Puerto Rico now have laws in place to reduce light pollution.
Astro-tourism is the impetus for some regions to eliminate light pollution and enhance star gazing. The Yorkshire Dales National Park in the United Kingdom has been running dark skies festivals since 2016 and was designated by the IDA as a “dark sky reserve” in 2020. For ecological, health, and resource protections, many European countries have implemented programs and laws that reduce light pollution.
In 2002, the Czech Republic became the first member of the European Union to have a national law dedicated solely to reducing light pollution. Slovenia followed in 2007, requiring outdoor lighting to be shaded and below certain levels of brightness. Croatia and France introduced laws to restrict outdoor light levels in 2019. In 2021, France went further to enact some of the most progressive regulations around outdoor lighting. Catalonia, Scotland, Northern Ireland, and others are also quashing the problem.
In Norway, elimination of some excess lighting is being accomplished with smart streetlights. Like motion detector lights on buildings, streetlights are designed to detect an approaching vehicle, illuminate in succession as the vehicle safely passes, and then go off again.
Individuals are also acting by closing curtains at night so interior light doesn't spill into naturally dark spaces, lighting only what needs to be lit, and focusing security lights appropriately.
Modern life requires the benefits of lighting, but we now know it must be used more responsibly as it is harmfully disrupting natural daily and seasonal cycles in myriad organisms. Legislators, city planners, property owners, and citizens need to “see the light” and work to install systems and implement practices to reduce light pollution worldwide. As the movements grow to embrace the darkness, one day we will all be able to see the Milky Way, save natural resources, better protect our health, and preserve plants and animals subjected to our bright ideas.
*Julie Peterson writes on health and environmental issues from the Midwestern United States.