The body clock resets each day mainly through bright light entering the eyes in the morning. Getting 10 minutes of outdoor light within the first hour after waking is one of the cheapest, most evidence-backed sleep interventions available — and it typically outperforms complicated bedtime routines.
Morning light suppresses melatonin, sets the timing of the next melatonin release ~14 hours later, and raises cortisol at the correct hour. Missing this signal makes bedtime drift later and daytime energy less reliable.
5–10 minutes on a clear day, 15–20 on overcast, ideally within 30–60 minutes of waking. Outdoor cloudy light is roughly 10,000 lux; even the brightest office is 500 lux. Glass windows filter out much of the useful spectrum, so getting outside beats sitting by a window.
Pair the walk with something you already do (coffee, dog, trash), leave the phone charging out of the bedroom, and protect the evening half by dimming lights after sunset. Most people notice easier wake-ups within 3–5 days.
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