Exposure to artificial blue light at night reduces the production of melatonin and prevents the normal nighttime drop in cortisol levels.

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.

Being around too much blue light at night, like from phones or lamps, can mess with your sleep and your body's internal clock, making it harder to fall asleep and feel rested.

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.

Too much blue light messing with your sleep clock might also be bad for your mood, brain, and metabolism — not just your sleep.

Exposure to blue light from LEDs at a specific wavelength and brightness for three hours reduces the hormone melatonin in the saliva of healthy adults, and this reduction lasts longer than when exposed to red light at the same brightness.