Get bright light early in the day

Get outside daylight in the first hour or two after waking to set your clock.

Why it works

Specialized retinal cells signal the master clock based on light, and morning light advances the clock and suppresses residual melatonin — telling your body "day has started." This sharpens daytime alertness and, by setting the phase, pulls sleepiness earlier in the evening. Outdoor light is far brighter than indoor lighting, so it does the job in minutes.

How to do it

1. Get outside within an hour or two of waking, ideally 10–30 minutes.
2. On dark mornings, sit near a bright window or use a bright light source; outdoor light is still best.
3. Skip sunglasses for the exposure window so enough light reaches the eyes (never look at the sun directly).

Evidence

Light is the dominant zeitgeber for the human circadian clock, and morning bright light reliably advances circadian phase and improves daytime alertness in controlled studies. (rct)

Timing and dose matter; light at the wrong time can shift the clock the wrong way. Bright-light therapy for mood disorders is a separate clinical use.

Sources

• Czeisler et al. (1989), bright light resetting of the human circadian pacemaker, Science

Common mistake

Treating any indoor light as equivalent. Typical room lighting is a fraction of outdoor intensity and gives a much weaker signal.