Protocol
Morning sunlight: how many minutes you actually need.
The dose is smaller than you think. Roughly ten minutes outside on a bright morning, twenty to thirty under clouds, ideally within an hour of waking. What that buys is not vitamin D. It is the daily setting of the master clock that times your energy, mood, and sleep.
Does it work through a window?
Mostly no, and intensity is the reason. Glass passes the blue wavelengths your clock reads, but it cuts how much of them arrive, and sitting back from the window cuts the lux again. Ten minutes on the doorstep beats an hour behind glass.
Two practical notes. Never stare at the sun; brightness in your field of view is enough. And sunglasses defeat the purpose on the morning walk, while sunscreen does not. The signal enters through your eyes, not your skin.
What the evidence says it buys you
Bright light therapy for seasonal depression carries an effect size around 0.84, in the range of antidepressant trials, and helps non-seasonal depression as an adjunct. Brain serotonin turnover rises with the day's duration of bright sunlight. And the mirror-image experiment, bright screens at night, delays the clock by about an hour and a half and cuts REM sleep.
The evening half of the deal
From two hours before bed: warm lamps instead of overheads, screens dimmed, bedroom truly dark. The clock is set by contrast, bright days and dark nights, and modern life supplies the exact opposite. Flip both and most people feel the difference inside a week.
Written by Kyle Jenkin · updated August 31, 2026 · how we grade evidence
Ten minutes, before the day takes you. The clock is waiting.
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