A Human Web
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The atlas · Chapter three · practice two of five

Days too dim and nights too bright flatten the rhythms that time serotonin, melatonin, and cortisol. The fix is almost embarrassingly simple, and it starts within an hour of waking.

Sunlight, the second practice.

The repair protocol for a body clock kept indoors: bright mornings, outdoor minutes, dim evenings. Plus the honest answer on whether vitamin D pills substitute for the sun.

Practice 02 · Sunlight

Your eyes need lux. Your skin needs limits.

Every cell in your body runs on a clock set by bright light reaching your eyes. Days too dim and nights too bright flatten it. The repair is almost embarrassingly simple: bright mornings, dim evenings.

101001K10K100KLUX, LOG SCALELIVING ROOM, EVENING50OFFICE LIGHTING500where we spend ≈87% of our hoursOVERCAST DAY, OUTSIDE10KCLEAR DAY, SHADE25KDIRECT SUMMER SUN100Kwhat your body clock evolved to expect
Fig. 05 · light your eyes receive, on a log scale

Start today

  • Get outside within an hour of waking, most days: ~10 minutes bright, 20–30 overcast. Even a grey sky delivers about 20× office light.
  • Work near a window and bank daylight with outdoor breaks. Aim for two hours a week in green space.
  • From two hours before bed: warm lamps, low light, screens winding down. Keep the bedroom truly dark.
  • Never burn. Shade, clothing, SPF 30+ for extended sun. The circadian benefit enters through your eyes, and sunscreen doesn't block it.
File under hype

“Vitamin D pills give you what sunlight would.”

The largest trial ever run (18,353 adults, five years) found vitamin D supplements did not prevent depression or improve mood. Correct a deficiency for bones and immunity. But low vitamin D is partly a marker of a low-light life. It's the light itself doing the mood work.

read the full verdict →

What the evidence says

0.84
effect size for light therapy in seasonal depression
1.5 hrs
body-clock delay after five evenings of screen reading
120 min
a week in green space: the wellbeing threshold
20×
more light outside on a grey day than in an office

Modern life keeps us at roughly 87% indoors, under lighting 20 to 200 times dimmer than an overcast sky. Days too dim and nights too bright flatten the rhythms that time serotonin, melatonin, and cortisol.

  1. Bright light therapy for seasonal depression has an effect size of ~0.84, in the same range as antidepressant medication trials. It helps non-seasonal depression as an adjunct too.

    evidence · strongGolden 2005 · Lam 2016

  2. Brain serotonin turnover rises directly with the day's duration of bright sunlight, measured in blood draining from the brain.

    evidence · strongLambert, Lancet 2002

  3. Five evenings of screen reading before bed delayed the body clock about 1.5 hours, versus a printed book. It also suppressed melatonin, cut REM sleep, and impaired next-morning alertness.

    evidence · strongChang, PNAS 2015

  4. About 120 minutes a week in green space marked the threshold for better self-reported health and wellbeing in ~20,000 adults. Forest-bathing studies show lower cortisol and blood pressure.

    evidence · emergingWhite 2019 · Antonelli 2019

Go deeperMorning sunlight minutesVitamin D vs sunlightWhere light sits on a clock

The other four practices.

Same web, any order.

Practice 01

Movement

Small doses, all day.

Practice 03

De-stress

Two sighs at the spike.

Practice 04

Nutrition

Half the plate, plants.

Practice 05

Fascia care

Slow lines, then spring.

All five practicesA day, rewovenThe move databaseThe evidence ledger

Light sets the clock. The day page shows where it fits.

Find your thread →The 24-hour protocol

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