Why is bright light at night bad for sleep?

Bright light at night can suppress melatonin and signal your circadian clock to stay awake or shift later, making it harder to fall asleep and disrupting sleep timing. 1

• 1. After 8 PM: Even relatively small amounts of light can activate the clock more easily later in the day, encouraging a later bedtime and disrupting sleep patterns. 2
• 2. Between 10 PM and 4 AM: Bright light is especially concerning during this window; light exposure around these hours can suppress dopamine and affect mood, learning, and attention. 3