Late-day light

Do this

• In the last third of your day, spend 5–10 minutes outside without sunglasses. You don't need to see the sunset itself.
• If you work indoors until dark, move next to a window or walk once around the building.
• Overcast still counts. There is always more light outside than inside.

Why it works

Light you get during the day makes the eye's clock cells less reactive to artificial light later on. He calls this a Netflix inoculation: afternoon daylight softens the hit that melatonin, blood sugar and sleep take from evening screens. He adds that it doesn't seem to protect teenagers.

What the research says

Laboratory studies show that people who get more light earlier in the day lose less melatonin to the same evening light. The studies are small and measure melatonin, not long-term health.

• Hébert et al., Journal of Pineal Research, 2002The effects of prior light history on the suppression of melatonin by light in humansAfter a week of bright days, the same evening light suppressed melatonin less than after a week of dim days.
• Chang, Scheer & Czeisler, Journal of Physiology, 2011The human circadian system adapts to prior photic historyThree days in very dim light made the body clock more sensitive to a later light pulse than three days in ordinary room light.
• Crowley et al., Journal of Clinical Endocrinology & Metabolism, 2015Increased Sensitivity of the Circadian System to Light in Early/Mid-PubertyChildren in early puberty lost far more melatonin to evening light than older adolescents did.

Watch out

This softens the effect of evening screens. It doesn't cancel bright light late at night.