Why is bright light at night bad for sleep?

Exposure to bright light at night can disrupt our sleep because it interferes with our circadian rhythm, which is the body's natural sleep-wake cycle. Bright light exposure in the evening or at night can delay the production of melatonin, the hormone that signals our body it's time to sleep. Viewing bright light late in the day, especially between 10 PM and 4 AM, may shift our internal clock to a later schedule, making it harder to wake up early and go to sleep at a reasonable hour 1 2.

The neurons in our eyes that signal to our brain when it's daytime and when it's night are easily activated by light at night. This late-day sensitivity causes the brain to mistake night light for morning light, delaying sleepiness and altering hormone levels 3 4.

Therefore, it is recommended to avoid bright artificial light exposure in the middle of the night to maintain proper sleep hygiene and overall health 5.