The next day
Morning light: why the first hour of the day shapes the night ahead
The short answer
The light that reaches your eyes in the first hours after waking sets your body clock earlier, which is what makes you sleepy at a sensible time tonight. Daylight through a window helps; outside is better, even under cloud. It won't fix poor sleep by itself, but it's the cheapest lever you have.
The curtains are still shut, and it's November. You open them at 7.10am on a sky the colour of dishwater.
The garden is a pencil sketch of itself. You put the big light on; that's what it's for.
The commute is a car with the heater on, or eleven steps from the kettle to the laptop. You next look up at 1pm. You haven't been outside.
By 4.15pm it's dark again.
Nobody plans a day like that. It's what a British winter does to a working week. Your body clock notices, though.
It was expecting a sunrise. It got a ceiling light. Tonight it will run late, and tomorrow's 7.10am will feel like 6.10am.
What light does to your body clock
Behind your eyes sits a small cluster of cells that keeps time for the whole body. It's set each day by light, through a direct line from the retina. No other signal comes close.
Timing is everything. Light in the morning pulls the clock earlier; light in the evening and at night pushes it later.
That's the whole rule. Modern life breaks it both ways: dim days, bright nights.
The clock also controls melatonin, the hormone your body makes as night sets in. When the clock is set earlier, melatonin starts earlier, and so does feeling sleepy. That's the early night that arrives by itself after a day outdoors.
Does it have to be sunshine?
No, and this is the useful part for a grey country.
In 2022 an international group of light scientists set a daytime target. At least 250 lux at the eye, in units that weight light by how strongly the clock responds to it. Plenty of lit rooms fall short.
The same report notes that indoor lighting standards sit at least ten times below daylight outdoors. An overcast sky is still daylight, from every direction at once.
A few minutes on the doorstep gives you more than the window does, and the window gives you more than the ceiling light.
The evening limit in that report is 10 lux. That's about a dim lamp. A bright kitchen at 10pm and a dim desk at 10am: the clock reads both as "later".
What the evidence shows, at its true size
The big studies are surveys. In the UK Biobank, more than 400,000 adults reported a median of two and a half hours a day in daylight. Each extra hour went with finding it easier to get up, fewer insomnia symptoms and an earlier body clock.
Those are self-reports. People who spend more time outside differ in other ways too. When the same people were followed over time, the links held but were smaller.
A 2019 review adds a questionnaire finding: each hour spent outdoors came with sleep about 30 minutes earlier. Outdoor time comes bundled with exercise, though. Exercise moves the clock as well.
The trials are of light therapy, which usually means a bright lamp rather than the sky. A 2016 review pooled 53 light-therapy studies, 1,154 people in all.
It found small-to-medium effects on sleep problems, strongest for body-clock disorders and insomnia. There were also signs that positive results were the ones more likely to be published.
So the effect is real, and it's modest. Anyone selling morning light as a fix for everything hasn't read that review.
How to get morning light in a British winter
- Open the curtains before you do anything else. The clock starts reading light the moment your eyes open. A November window at 7am is dim, but it isn't nothing. The NHS self-help guidance puts it simply: light tells the brain it's time to wake up. If mornings are the hard part, the first half hour has its own article.
- Get outside in the first two hours, even for five minutes. Daylight outdoors is far brighter than a lit room, cloud or no cloud. The doorstep with a cup of tea counts. So does the long way to the car.
- In midwinter, take the dose when the sun is actually up. The British Sleep Society's figures put sunrise at the winter solstice just after 8am in London and nearer 8.45am in Glasgow. If you leave in the dark, the first daylight you can reach is the one that counts. Lunch by a window, or ten minutes round the block at noon.
- Keep the evening dim. The rule runs both ways, and the 2022 target for the three hours before bed is 10 lux. Lamps rather than the big light, and the screen turned down. There's more on this in how to wind down before bed.
- Pair the light with a fixed wake-up time. Light sets the clock to whenever it arrives. If that hour moves around, so does the clock, which is why the wake-up time matters more than bedtime.
What more light won't change
If you already fall asleep at a reasonable hour and wake without a fight, more morning light won't change much. The trials were done in people with sleep problems. What light moves is the clock.
It does nothing for last night, either. Light works on tonight and the nights after, a little at a time. Give it a week before you decide.
You can't do much about a November sky. You can decide where you'll be standing under it, and when.
Read next
The evening
Why your wake-up time matters more than your bedtime
The next day
How to wake up feeling refreshed
The evening
How to wind down before bed
Questions
What are the benefits of morning sunlight for sleep?
Morning light pulls your body clock earlier, so melatonin and sleepiness arrive earlier that night. In the UK Biobank, each extra hour of daylight went with easier mornings and fewer insomnia symptoms. The effect in trials is modest; think of it as a lever, not a switch.
What time should you get morning sunlight?
In the first couple of hours after waking; that's the light that pulls the clock earlier. In midwinter that may be before sunrise, so take the first daylight you can reach instead. Light at lunchtime still counts towards the daily total.
Does morning sunlight need to be in your eyes?
Light has to reach your eyes, which only means being out in it with your eyes open. Never look at the sun. Indoors by a window gets you part of the way; outside gets you all of it.
Does morning light work on a cloudy day?
Yes. Cloud cuts daylight a long way, and it's still well above a lit room; the 2022 report puts indoor lighting standards at least ten times below daylight outdoors. The sky changes how the morning feels more than what your clock receives.
Sources
- Sleep problems and insomnia self-help guide, NHS inform, 2021
- Effects of light on human circadian rhythms, sleep and mood, Somnologie, 2019
- Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults, PLoS Biology, 2022
- Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: a cross-sectional and longitudinal study in over 400,000 UK Biobank participants, Journal of Affective Disorders, 2021
- The effects of light therapy on sleep problems: a systematic review and meta-analysis, Sleep Medicine Reviews, 2016
- The British Sleep Society position statement on Daylight Saving Time in the UK, Journal of Sleep Research, 2024
This article is general information, not medical advice. If sleep problems last more than a few weeks, speak to your GP.
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