You’ve heard of air pollution and water pollution. Now, scientists are saying there’s another kind of pollution that may also be harmful to your health: light pollution.
Light pollution (which scientists more specifically call artificial light at night, or ALAN) affects nearly every American. And it’s getting worse, with an average yearly increase of about two percent in artificially lit outdoor areas and in the brightness of continuously lit areas. Plus, an increasing number of Americans—an estimated 5 to 10 percent—work night shifts.
What causes light pollution? There are many sources, indoors and out.
Indoors:
- Screen devices, like smartphones, tablets, computers, and
televisions. These emit blue light, a short wavelength light that is good for health in the daytime, when it’s energizing, but bad for health in the nighttime, when it can disturb sleep.
- LED, fluorescent lighting, and compact fluorescent light bulbs,
all of which emit predominantly blue light, and are the predominant lighting in hospitals, fire stations, and other places where shift work is common.
- Nightlights and appliance lights.
Outdoors:
- Streetlights, particularly the blue light from mercury vapor lights.
- Exterior lighting on buildings.
- Lights left on overnight in tall buildings in cities.
- Headlights from traffic.
- Advertising and digital billboards.
- Parking lot and stadium lighting.
- Public spaces and pathway lights.
Breaking the circadian clock
For many decades, scientists thought artificial light at night was as harmless as the stars and moon. More recently, they have discovered that ALAN is a health-damaging pollutant—mainly because it resets your circadian clock.
The circadian clock is a gene-driven, cell-based system that regulates every function of the body in response to the 24-hour cycle of day and night—in particular, the various wavelengths of light, like the longer wavelengths of sunrise and sunset (orange/red/yellow), and the shorter wavelengths of midday blue light.
When the circadian clock is reset by exposure to artificial light at night, the functions of the body are disturbed—and health problems may be the eventual result. Disturbed circadian rhythms have been linked to:
- insomnia
- depression and anxiety
- high blood pressure, heart attack, and stroke
- type 2 diabetes and obesity
- chronic inflammation, which contributes to many chronic diseases
- autoimmune disease
- prostate and breast cancer
- irritable bowel syndrome and heartburn
- infertility and polycystic ovary syndrome
Recent research shows how much light pollution increases your risk for poor health.
More cancer. A study published in the December 2024 issue of The Science of the Total Environment analyzed data from more than 730,000 women and found that high levels of exposure to artificial light at night was linked to a 12 percent increase in the risk of breast cancer. The researchers also linked ALAN to non-Hodgkin lymphoma, colorectal, pancreatic, and thyroid cancer.
More depression. In an April 2025 study by an international team of researchers, data from more than 550,000 people showed that bedside light at night increased the risk of depression by 45 percent, and overall light at night overall increased risk by 18 percent. It also increased the risk of anxiety and bipolar disorder. “…our results suggest that LAN exposure influences adverse mental health conditions,” wrote the researchers.
More obesity and heart disease. In an April 2025 study in the American Journal of Epidemiology, outdoor artificial light at night was linked to a 29 percent increased risk of obesity, a 73 percent increased risk of hemorrhagic stroke, a 17 percent increased risk of high cholesterol, and a 55 percent increased risk of angina in women.
Restore your rhythm
There are many ways to reduce light pollution and protect your circadian clock.
Use blackout curtains
They block 98 to 100 percent of outdoor light. (Room darkening or “light filtering” curtains block only 70 to 90 percent.) The best materials are polyester, microfiber, or triple-weave fabric. Multi-layered curtains with foam backing or light-blocking liners perform well. To prevent light seepage, the curtains should be a few inches wider than the window on each side, hang close to the ceiling, and extend past the frame. If you don’t want to buy new curtains, try blackout liners to attach to your existing curtains.
Wear a sleep mask
Look for a mask labeled “100% blackout” or “lightproof.” If you’re a side sleeper, look for a contoured mask that is molded to fit around the eyes without pressure on your eyelids or lashes. If you’re a back sleeper, look for a flat mask. Natural materials are best, like mulberry silk, cotton, or bamboo.
Take melatonin before bedtime
Light pollution can block the production of melatonin, which regulates the body’s circadian rhythm. Consider taking 3 to 5 milligrams (mg), a couple of hours before bedtime.
In the evening, wear blue light blocking glasses
Screens—smartphones, computers, TV, video games—generate blue light. The best advice is to not use screens at night, stopping an hour or two before bedtime. But that’s advice few people actually follow. If you must use devices at night, wear blue light blocking glasses, which use amber- or orange-tinted lenses to filter out blue wavelengths. Research shows that wearing blue-blocking glasses for 2 to 3 hours before bed can preserve melatonin levels and improve sleep quality.
Use new, light-reducing technology on your devices
Apple (iPhone, iPad, Mac) offers Night Shift, which shifts the screen’s color away from blue and toward warmer, orangish tones. You can find it under Settings, either scheduling it, or turning it on manually. The “Dark Mode” setting on Android, Windows, and Apple reduces light emission. There are also several blue light filtering apps, like f.lux, Iris, and Twilight.
Switch your lighting at home
Replace cool-white or daylight LEDs with warm-white bulbs in bedrooms and living spaces. Use smart bulbs (like Philips Hue or LIFX) that allow scheduling and color adjustments. Use red or amber nightlights, which have minimal circadian impact.
Try time-restricted eating
Eating all of your meals within an 8- to 10-hour period, and no meal later than 6 pm, can help maintain circadian rhythms. For example, eat breakfast at 8 am and dinner at 5 pm.
