Why is bright light at night bad for sleep?

Bright light at night is detrimental to sleep because it disrupts the release of melatonin, the hormone responsible for inducing sleepiness and facilitating sleep. Andrew Huberman advises avoiding bright lights, especially overhead lights, between 10:00 p.m. and 4:00 a.m. to ensure good sleep quality and maintain sleep-wake cycles 1. These bright lights mimic sunlight, which interferes with the natural circadian rhythms by activating alertness neurons in the eye that are usually stimulated by sunlight during the day 2.

Bright light in the middle of the night, even if not extremely bright, can suppress dopamine release, which is essential for mood regulation and can impact learning and contribute to a decrease in mood and learning capacity 2. This exposure to light during typical sleeping hours has also been linked to disturbances in metabolic processes, including blood sugar regulation, further emphasizing the importance of avoiding bright light during these times 3.

To protect against these negative effects, Dr. Huberman recommends reducing the intensity of light exposure at night and utilizing light sources placed lower in the visual field 3. Additionally, afternoon light viewing helps to decrease the eyes' sensitivity to light at night, providing some leeway in regard to screen lights and other light exposure without disrupting the circadian clock 4.