Donate Join

Human Health

Many species (including humans) need darkness to survive and thrive.” — American Medical Association Council on Science and Public Health (2012)

Exposure to Artificial Light at Night Can Harm Your Health

Humans evolved to the rhythms of the natural light-dark cycle of day and night. The spread of artificial lighting means most of us no longer experience truly dark nights.

Research suggests that artificial light at night can negatively affect human health, increasing risks for obesity, depression, sleep disorders, diabetes, breast cancer and more.

Circadian Rhythm and Melatonin

Like most life on Earth, humans adhere to a circadian rhythm — our biological clock — a sleep-wake pattern governed by the day-night cycle. Artificial light at night can disrupt that cycle.

Our bodies produce the hormone melatonin in response to circadian rhythm. Melatonin helps keep us healthy. It has antioxidant properties, induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands. Nighttime exposure to artificial light suppresses melatonin production.

Not All Artificial Light Is Created Equally

Exposure to blue light at night is particularly harmful. Unfortunately,most LEDs used for outdoor lighting — as well as computer screens, TVs, and other electronic displays — create abundant blue light.

To minimize harm from blue light, choose the right light bulb and download a color temperature app that adapts your electronic screen to the time of day – cool light during the day and warm light at night.

Color Temperature Apps:

  • F.lux is available for Mac OS/X, Windows, Linx, iPhones and iPads
  • Lux is available for Android devices free or for pay
  • Twilight is available for smartphones or tablets

Choosing the Right Bulb

ColorTempIn the picture on the left, the bulb on the left is rich in high-color temperature blue light, while the one on the right isn’t.

Be sure to look at the packaging. All packaging for new CFL and LED light bulbs provide color temperature information. Use low color temperature light sources for interior and exterior light. Their light is less harsh and less harmful to human health and the environment. Look for warm white sources with a color temperature of 3500K or lower.

The Kelvin temperature chart below shows you what the numbers mean.

Kelvin Temperature Scale

Higher color temperatures mean bluer light, the kind that should be avoided after dusk.

Kelvin Temperature Scale


Read our Seeing Blue Report to learn more.

Glare from Bad Lighting is a Safety Hazard

Glare from poorly shielded outdoor lighting is also harmful to your health, because it decreases vision by reducing contrast. This limits our ability to see potential dangers at night. Aging eyes are especially affected.

“Glare from nighttime lighting can create hazards ranging from discomfort to frank disability.” — American Medical Association Council on Science and Public Health (2012)