Can morning light help you sleep better?
What the research found, how to do it, and every source the episode cites.
The verdict
Try it for two weeks.
- When
- you get up
- Then
- go outside for 30 minutes
§ 01 · The protocol
§ 02 · Transcript
- The question
Can morning light help you sleep better?
- How it works
Your body clock is a timer in your brain. Two hours before bedtime, it starts releasing melatonin, the signal that night has come. It also times cortisol, which climbs after you wake. But it's like a watch that loses nine minutes a day. Morning light puts it back on time. Light at night makes it lose more.
- The research
In the lab, an hour of morning light moved the clock earlier. The same hour, at night, moved it four times as far the other way.
- The protocol
Get bright light within an hour of waking, for thirty minutes. Outside beats indoors, even when cloudy. Then keep evenings dim.
- The verdict
Do that, and your clock stays on time. Try it out for two weeks, and track it with Anvilus.
§ 03 · In the sources' words
“in most people it must be reset by a small phase advance shift each day”
“Following the week of exposure to natural lighting, all measured markers of internal circadian time were ~2h earlier”
“the single 30-minute bright light exposure was as effective as 1 hour of bright light spread over 3.25 h, and produced 75% of the phase shift observed with 2 hours of bright light”
“on an overcast day, it is approximately 15,000 lux”
“starting at least 3 hours before bedtime, the recommended maximum melanopic EDI is 10 lux”
“very close to 24 h [24.15 ± 0.2 h (24 h 9 min ± 12 min)]”
§ 04 · Sources
- Duffy JF, Czeisler CA. Effect of light on human circadian physiology. Sleep Med Clin 2009;4(2):165
- St Hilaire MA et al. Human phase response curve to a 1 h pulse of bright white light. J Physiol 2012;590(13):3035–3045
- Crowley SJ, Eastman CI. Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright-light duration? Sleep Med 2015;16(2):288
- Tähkämö L, Partonen T, Pesonen AK. Systematic review of light exposure impact on human circadian rhythm. Chronobiol Int 2019;36(2):151–170 (open access, author repository copy of the version of record)
- Wright KP Jr et al. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol 2013;23(16):1554–1558
- Stothard ER et al. Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Curr Biol 2017;27(4):508–513
- Ohashi M et al. Relationship between circadian phase delay without morning light and phase advance by bright light exposure the following morning. Clocks Sleep 2023;5(4):615–626
- Revell VL et al. Advancing human circadian rhythms with afternoon melatonin and morning intermittent bright light. J Clin Endocrinol Metab 2006;91(1):54–59
- Khanal S et al. IOVS 2025;66(7):7 (secondary statement on typical light levels)
- Blume C, Garbazza C, Spitschan M. Effects of light on human circadian rhythms, sleep and mood. Somnologie 2019;23:147–156
- Brown TM et al. Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLoS Biol 2022;20(3):e3001571
- Duffy JF et al. Sex difference in the near-24-hour intrinsic period of the human circadian timing system. PNAS 2011;108(Suppl 3):15602–15608
- Eto T, Higuchi S. Review on age-related differences in non-visual effects of light: melatonin suppression, circadian phase shift and pupillary light reflex. J Physiol Anthropol 2023;42:13
- Dautovich ND et al. A systematic review of the amount and timing of light in association with objective and subjective sleep outcomes in community-dwelling adults. Sleep Health 2019;5(1):31 (funded by the National Sleep Foundation)
- Nagare R et al. Access to daylight at home improves circadian alignment, sleep, and mental health in healthy adults: a crossover study. IJERPH 2021;18(19):9980 (funded by View Inc., the glazing maker)
- Bowles NP et al. The circadian system modulates the cortisol awakening response in humans. Front Neurosci 2022;16:995452
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