Why is bright light at night bad for sleep?

Bright light at night is detrimental to sleep because it can disrupt the body's circadian rhythms and suppress the natural release of melatonin, a hormone that promotes sleepiness. Exposure to light in the late hours can therefore significantly affect your ability to fall asleep and maintain sleep. Andrew Huberman explains that bright artificial lights, particularly overhead lights, should be avoided from 10:00 p.m. to 4:00 a.m. since they can delay your internal clock, making it harder to wake up early and go to bed early 1.

Furthermore, bright light exposure to the eyes between 11:00 p.m. and 4:00 a.m. has been shown to suppress the release of dopamine, a neurotransmitter that contributes to feeling good and can influence learning and mood 2. This means that exposure to bright light during these hours could potentially affect not only your sleep but also your mood and cognitive function.

For sleep optimization and mood improvement, it is recommended to experience bright light, ideally natural sunlight, during the early part of the day and to avoid bright artificial light exposure at night 3.