Morning sunlight
10 minutes outdoors within an hour of waking anchors the circadian rhythm.
Why
Bright outdoor light in the first hour after waking suppresses melatonin and sets the body's internal clock for the day, making evening sleep onset easier. Cloudy days still deliver several thousand lux outdoors, far more than typical indoor lighting.
Slot in your day
How to do it
How
10–15 minutes outdoors, preferably without sunglasses, ideally walking. Light therapy lamps (10,000 lux) work as a substitute when outdoors isn't possible.
Sticking with it
Pair it with a fixed morning anchor: coffee, walk, school run. The pairing carries the habit.
Markers this may influence
Evidence
Wright 2013 Curr Biol (n=8): one week of camping with no electric light advanced melatonin onset by ~2 hours and aligned circadian phase with the natural light/dark cycle: small but mechanistic confirmation that morning bright light is the dominant entraining signal. Khalsa 2003 mapped the human phase-response curve to single bright-light pulses.