What is the circadian rhythm and how does it affect sleep?

Short Answer

The circadian rhythm is your internal 24-hour clock that regulates sleepiness and alertness. Light is its strongest cue, so morning light advances your schedule and evening light can delay sleep timing.

Why This Matters

This matters because sleep isn’t only about “how tired you are”—it’s also about biological timing. When your schedule conflicts with your clock, it results in insomnia at bedtime and sleepiness during the day. Aligning light, meals, and wake time leads to more consistent sleep onset and better energy.

Where This Changes

Chronotype differs—some people naturally run later or earlier—so the “ideal” bedtime depends on your wake time. Shift work, jet lag, and late-night screens can override cues and create circadian misalignment that needs structured light management to correct.