Sunmaxxing, explained: a science-based guide to morning sunlight

What is sunmaxxing?

Sunmaxxing started as a trend for getting as much sun as possible. The version worth keeping is circadian sunmaxxing: the habit of getting outside within about an hour of waking, so natural daylight reaches your eyes.

It’s about your eyes, not your skin. Nothing in this guide needs UV, a tan or long hours in strong sun — daylight from the whole sky does the work.¹

Why morning light matters

Daylight reaching your eyes is the main signal that sets your body clock — helping you feel awake by day and sleepy at night.¹

Timing matters. In laboratory studies, light in the biological morning shifts the clock earlier, while bright light late in the evening can push it later.²³

Real life agrees. After a week of camping with only natural light, people’s body clocks moved earlier and lined up with sunrise and sunset.⁴

An international expert consensus recommends at least 250 lux of melanopic light at the eye during the day — ideally from daylight.¹

How bright is outdoor light?

Outdoors is in a different league from indoors. Even on an overcast day, outdoor light is usually 1,000 lux or more — several times brighter than a well-lit room (100–500 lux).⁵

The table shows how outdoor light grows as the sun climbs, from Soltide’s sun engine. These are estimates for open ground, not measurements: what reaches your eyes is usually lower.

How long should you stay out?

There’s no validated daily light “dose” for healthy adults. The body clock’s response levels off as light gets brighter, and it doesn’t grow in a straight line with time — so a brighter morning doesn’t mean you can stay out for much less.⁶⁷

Soltide uses a light goal of about 30 minutes of bright outdoor light. It’s a habit target borrowed from bright-light research, not a clinical dose. On grey days the goal stays the same; Soltide just looks for the brightest time you can get out.

Sunmaxxing in winter

In the dark months the window is short, and a grey sky hides much of it. Around the shortest day, northern cities get only a few hours of daylight, and the sun stays low:

Grey days still count

Even under cloud, outdoor light is usually far brighter than indoors. Morning light matters most for your body clock, but if your mornings are dark or busy, a walk in the brightest part of the day is a good option — later daylight may still help.⁸

Light, not a tan: UV and vitamin D

Never look directly at the sun. You don’t need to: light from the whole sky reaches your eyes.

When the UV index reaches 3, protect your skin: seek shade, cover up with clothing and a hat, wear sunglasses and use SPF 30+. Sunscreen isn’t a reason to stay out longer. Clouds cut UV less than they cut visible light, so a grey day can still need protection.⁹

In winter, above about 40°N, the sun is too low for your skin to make much vitamin D — often very little.¹⁰ Many health agencies recommend a supplement in these months, and some people all year — ask a doctor or pharmacist.¹¹

The other half: dim evenings

Light works both ways. The same expert consensus recommends keeping light at the eye low in the evening, starting at least three hours before bed.¹ In practice: dim the lights 2–3 hours before bed.

A simple morning routine

• Step outside within about an hour of waking, or as soon as you can.
• Aim for about 30 minutes outdoors. A walk counts; a grey sky counts.
• Look around at the sky and the street — never directly at the sun.
• If the morning is dark or busy, go out around midday instead.
• From UV 3, protect your skin.
• Keep your evenings dim.

Sources

1. Brown TM, Brainard GC, Cajochen C, et al. (2022). Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLOS Biology 20(3): e3001571. doi:10.1371/journal.pbio.3001571
2. Khalsa SBS, Jewett ME, Cajochen C, Czeisler CA (2003). A phase response curve to single bright light pulses in human subjects. The Journal of Physiology 549(3): 945–952. doi:10.1113/jphysiol.2003.040477
3. St Hilaire MA, Gooley JJ, Khalsa SBS, et al. (2012). Human phase response curve to a 1 h pulse of bright white light. The Journal of Physiology 590(13): 3035–3045. doi:10.1113/jphysiol.2012.227892
4. Wright KP Jr, McHill AW, Birks BR, et al. (2013). Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology 23(16): 1554–1558. doi:10.1016/j.cub.2013.06.039
5. Oldham MA, Oldham MB, Desan PH (2019). Commercially available phototherapy devices for treatment of depression: physical characteristics of emitted light. Psychiatric Research and Clinical Practice 1(2). doi:10.1176/appi.prcp.2019.20180011
6. Zeitzer JM, Dijk DJ, Kronauer RE, Brown EN, Czeisler CA (2000). Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. The Journal of Physiology 526(3): 695–702. doi:10.1111/j.1469-7793.2000.00695.x
7. Chang AM, Santhi N, St Hilaire M, et al. (2012). Human responses to bright light of different durations. The Journal of Physiology 590(13): 3103–3112. doi:10.1113/jphysiol.2011.226555
8. Lok R, Smolders KCHJ, Beersma DGM, de Kort YAW (2018). Light, alertness, and alerting effects of white light: a literature overview. Journal of Biological Rhythms 33(6): 589–601. doi:10.1177/0748730418796443
9. World Health Organization (2002). Global Solar UV Index: A Practical Guide. WHO, WMO, UNEP, ICNIRP. iris.who.int/handle/10665/42459
10. Webb AR, Kline L, Holick MF (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3. The Journal of Clinical Endocrinology & Metabolism 67(2): 373–378. doi:10.1210/jcem-67-2-373
11. NHS (2026). Vitamin D. nhs.uk. www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/

This guide was written by the Soltide team with AI assistance, from the peer-reviewed studies and official guidance listed above, and checked against Soltide’s medical and legal review. The tables come from Soltide’s sun engine, the same code as in the app.

Soltide offers general wellness information, not medical advice. Light levels are estimates. If you have health concerns, talk to a doctor.