By Nina Capaldi ’27
Light pollution is the human-made change to outdoor light levels. Factories, streetlights, billboards, houses, parking lots, and satellites all contribute to light pollution. Light pollution is a serious concern as the brightened sky is detrimental to all life. Two-thirds of America and over a half of Europeans can no longer view the Milky Way with their naked eyes, and 63% of the world population and 99% of the E.U. and U.S. live under a night sky that is brighter than the threshold for light-pollution. According to the International Astronomical Union, the threshold for light pollution is if the artificial brightness of the sky is greater than 10% of the brightness of the natural sky. Light pollution has gone unchecked for years, and has increased by 10% every year since 2011. But the impacts of light pollution exceed far beyond the sky.
Artificial light sources can disrupt human circadian rhythms, or our internal clocks that regulate our sleep cycles by responding to light changes. This system is crucial for our health, but disruptions can occur when our clock is out of sync. Shift work and lights at night cause circadian changes, and studies have linked these disruptions to increased risks of cancer. Furthermore, our risk of obesity, mood disorders, and reproductive problems is increased. Disruptions occur due to the exposure to light at night. Light pollution suppresses the human body’s natural production of melatonin, which is a crucial hormone that regulates our sleep-wake cycle. If lower levels of the hormone are produced, people will experience disrupted sleep patterns. Long-term effects of sleep loss include risk of diabetes, depression, and stroke.
Artificial lights have detrimental impacts on the environment as well. For instance, light pollution disrupts bird’s migratory paths. Bright lights attract the animals, leading to collisions with structures. It is estimated that over 1 billion migrating birds are killed from these accidents. 80% of North American birds migrate at night and depend on the moon’s light to navigate. Light pollution, however, drowns out natural light. Bright lights also negatively impact birds’ migratory stopover habits. Birds can become trapped in bright areas, circling endlessly and burning important energy stores. They also have difficulty hunting when lights illuminate their surroundings.
Of the insects attracted to artificial lights at night, about a third die. Increased night brightness also means insects hatch at incorrect intervals, and those that do hatch have stunted development because of their negatively altered circadian rhythms and metabolic functions. Light pollution negatively impacts billions of insects by exhausting them, hindering their ability to navigate, and increasing predation. The whole ecosystem is affected by this endless day. Biodiversity has, and will continue to, decrease, meaning the food, medicine, and materials we harvest from nature will be depleted. Biodiversity also increases the resilience of areas against natural disasters. However, these regulations which we depend on are affected by disruptions to the natural food web.
Light pollution has reduced the number of pollinator visits to flowers by 62%. Artificial lights have delayed, and sometimes eliminated, nocturnal insect mating. 100 billion insects die every summer in Germany alone. In the next several decades, it is estimated that 1 million species, including around 40% of insects, will go extinct due to human actions. Other animals are affected by light pollution as well, including sea turtles, frogs, hummingbirds, zebrafish, seabirds, monarch butterflies, Atlantic salmon, zooplankton, bats, owls, fireflies, and more.
There are technological solutions to this problem, such as shielded lights. The light fixtures are built to block light from illuminating the sky. Streetlights installed with these reflectors prevent light from traveling far, emitting a disorienting glare, and unnecessarily lighting up the sky. However, shielded lights can have drawbacks. For instance, in areas covered by snow, the directed light will reflect back up to the sky. The clouds that last for 90% of winter act as reflectors as well, and can cancel out the benefits of shielded lights. Still, while shielded lights are not 100% effective, they are able to counter some of the effects of light pollution.
Another solution is switching from blue and white lights to warmer tones, which have a less negative effect on our circadian rhythms. Low-pressure sodium, high-pressure sodium, and low-CCT LEDs are good blue light substitutes. Filtered LEDs are also a good substitute for white lights. These bulbs reduce light pollution, and will save countless lives.
Many cities have sought ways to counter the effects of light pollution. The U.S. has passed many such laws. In 1958, Arizona passed the country’s first dark-sky ordinance. This ordinance banned the use of commercial searchlights. In 2020, 18 U.S. states, the District of Columbia, and Puerto Rico enforced laws to reduce light pollution. Called “dark skies” legislation, these laws promote energy conservation, public safety, and astronomical research capabilities. This legislation enforces the installation of shielded light fixtures, and encourages the use of low-wattage lighting.
Other countries have passed similar legislation. In the U.K., the All-Party Parliamentary Group for Dark Skies has published ten Dark Sky Policies to combat light pollution. Their regulations include setting standards for the direction of outdoor lighting. In 2023, Shanghai became the first Chinese city to legislate against light pollution, and Lanshan county shut down 2,500 street lights after 9 pm during the migratory season. Additionally, India has created Dark Sky Parks, such as the Pench Tiger Reserve in Maharashtra, which was certified by the International Dark-Sky Association in 2024. The park is designed around an observatory that restricts artificial lights, and they have done significant work around dark sky-friendly retrofits, night sky monitoring, and education about light pollution.
Despite these international efforts, light pollution is still very much a problem. However, individual acts, such as switching out bulbs or installing shielded light fixtures, can make a big difference to this universal problem. As light pollution continues to drastically increase, more measures are needed to be implemented to save what is left of our skies.
Read more articles like this in our Fall 2024 Issue!
