Light pollution is harming our health

“Watt for watt, blue light gives 10 times the effect of melatonin suppression as red,” says Mario Motta, a retired cardiologist who previously served on the American Medical Association’s Council of Science and Public Health, a group that first raised the alarm on light pollution more than a decade ago.

The impact of too much light at night is compounded by a lack of sufficient sun exposure during the day, since many people work in windowless offices or factories. “There’s a cumulative effect to not getting the proper doses of sunlight and darkness that we would have experienced over millennia as humans,” says John Hanifin, a neurologist and associate director of the Jefferson program.

Minority communities are especially at risk, due to the high wattage, outdoor “glare bombs” often placed near homes, says Travis Longcore, an urban ecologist at the University of California, Los Angeles. In a misguided effort to stem crime, these neighborhoods are lit more brightly than white neighborhoods. Excessive lighting “is an environmental justice issue,” Longcore says. 

Strong evidence for insomnia and cancer

A good night’s sleep is the most obvious casualty of excessive light. In brighter rooms, it’s harder to fall asleep. A study published in January also found that, among Chinese adults, bedroom light pollution makes sleep more fragmented, contributing to less total sleep time. 

These circadian rhythm disruptions can also increase levels of C-reactive protein, a sign of inflammation, along with other inflammatory markers, according to another Chinese study published online in June.

Excessive light exposure has also been linked to hormone-sensitive cancers, especially breast, colon, and prostate; epidemiological studies show that people living with the highest levels of light pollution tend to have higher rates of these cancers. Additionally, a 2023 study found that kids living in areas of California with bright outdoor lights were at greater risk for a form of childhood leukemia.

The leukemia finding “joins a growing body of research in epidemiology that associates cancer, even when controlling for other factors, to the outdoor light environment where people live,” says Longcore, an author of the study.

Not all epidemiological research supports a cancer link, including a large study in the United Kingdom. This may be because people’s exposure to outdoor lighting varies depending on bedroom location and window curtain thickness. 

Some people are also more sensitive to light pollution than others. One study found that when participants were exposed to light levels akin to that in the modern home, their melatonin dropped by 50 percent on average, but individuals exhibited more than 50-fold differences in sensitivity.

A wide range of health effects

Some smaller-scale, preliminary research raises the possibility of increased risk for heart disease, diabetes, and depression. A study this spring added ischemic stroke to the list of potential consequences.