How does light exposure affect sleep?

Short Answer

Light sets your circadian clock. Bright morning light helps you feel sleepy earlier at night, while bright evening light delays melatonin timing and can make it harder to fall asleep.

Why This Matters

This matters because many “sleep problems” are timing problems: your sleep drive and clock aren’t aligned. Morning light anchors the day, which leads to earlier melatonin release and stronger nighttime sleepiness. Evening light and screens result in a later clock and more insomnia-like symptoms even when you’re tired.

Where This Changes

Chronotype matters: night owls often benefit most from early bright light and reduced evening light. Shift work and winter darkness can require structured light therapy and consistent schedules to see meaningful changes.