Exposure to artificial light at night reduces the body's production of melatonin, a hormone involved in sleep regulation, and the more light a person is exposed to, the more melatonin is suppressed, regardless of the light source.

Exposure to artificial light rich in blue wavelengths (400–500 nm) during nighttime is linked to a greater reduction in melatonin levels in the blood of healthy adults compared to light with less blue content.

Higher levels of broad-spectrum light reaching the eye are linked to greater reductions in nighttime melatonin levels in healthy adults, with more light leading to more suppression.

Light that contains more blue wavelengths can reduce melatonin production at lower brightness levels than light with less blue, meaning it has a stronger biological effect for the same amount of light energy.

Being around blue light at night, like from phones or screens, might keep your body from making the sleep hormone melatonin because it keeps stress hormone levels high, making it harder to fall and stay asleep.

In healthy adults who have had limited sleep for two nights, exposure to blue light in the morning may shift the timing of melatonin release to occur earlier than when exposed to dawn-like or dim light.