Sleep Better

Lesson 4: Light and your body clock

Goal: use daylight to set your body clock, and keep evenings dim so it knows when night has arrived.

Light is the single strongest signal for your body clock. Special cells in the eye (using a pigment called melanopsin) report how bright it is to the brain’s master clock. Bright light in the morning tells it “day has started”; darkness in the evening lets the sleep hormone melatonin rise. Get those two signals right and falling asleep at night gets much easier.

A town still lit up at night beside a river, under a pink pre-dawn sky over the mountains. — The body clock's cue: first light. Photo: Murray Foubister, CC BY-SA 2.0

Morning: get daylight into your eyes

Go outside soon after waking and let daylight reach your eyes. Neuroscientist Andrew Huberman’s widely used rule of thumb, from his Toolkit for Sleep and his 2026 book Protocols, is:

within 30 to 60 minutes of waking
about 5 minutes on a clear morning, 10 minutes if it’s cloudy, and 20 to 30 minutes on a heavily overcast day
outdoors, not through a window, and without sunglasses if it’s comfortable and safe to do so
never look directly at the sun; just be outside facing the day

The principle (bright morning light anchors the body clock and makes you sleepy earlier at night) is well supported by research. One review describes a study in which each extra hour spent outdoors advanced people’s sleep timing by about 30 minutes. The exact minutes are Huberman’s practical guidance rather than tested thresholds, but they’re easy to follow. A walk, coffee on the balcony or the walk to the bus all count.

If you wake before sunrise, turn on bright indoor lights, then get outside once it’s light. A 10,000 lux light box is an option for dark winters or early shifts.

Daytime: brighter is better

Indoor light is far dimmer than daylight, even on a grey day. Getting outside during the day and working near a window both help keep the body clock’s “day” signal strong.

Late afternoon: catch the sunset

Huberman also recommends getting outside again in the late afternoon, around sunset. His view is that seeing the low, warm evening light tells the clock that the day is ending and may make you a little less sensitive to artificial light later on. The evidence for this part is thinner than for morning light, but it costs nothing and fits well with a walk after work.

For shift workers who sleep in the day, the logic is the same but shifted: get bright light during your “morning” (when you wake for a night shift), and treat the end of your shift as your “sunset” (see Lesson 12).

Evening: dim, warm and low

Dim the lights in the last two hours before bed. Use lamps rather than overhead lights.
Prefer warm, red-toned light. The body clock is most sensitive to blue light and least sensitive to red, so dim red or amber lamps at night disturb melatonin much less than bright white light.
Screens: a 2015 study found that reading on a light-emitting tablet for a few hours before bed delayed melatonin, made people take longer to fall asleep and left them less alert the next morning than reading a paper book. Night mode helps a bit; turning the brightness right down helps more; putting the device away helps most. What you’re doing on the screen matters too: work email and scrolling keep the mind busy.

Night: dark

Keep the bedroom properly dark (Lesson 6). If you get up in the night, use a dim night light rather than the main light.

Sleeping in late on days off shifts your body clock later, so Sunday night and Monday morning feel like jet lag. Researchers call this social jetlag. Keeping your wake time within about an hour of your weekday time, and getting morning light on weekends too, keeps the clock steady.

Watch

Everything you need to know about the circadian rhythm (Medical Centric Podcast)

Exercise 4

Tomorrow morning, get outside within an hour of waking for at least 10 minutes. Tomorrow evening, swap the main lights for lamps two hours before bed. Note how sleepy you feel at your target bedtime.

Sources

Blume, Garbazza & Spitschan (2019), Effects of light on human circadian rhythms, sleep and mood, Somnologie
Chang et al. (2015), Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness, PNAS
Andrew Huberman, Toolkit for Sleep and Protocols: An Operating Manual for the Human Body (Simon & Schuster, 2026)
Comparative effects of red and blue LED light on melatonin levels (2025)
Wittmann et al. (2006), Social jetlag, Chronobiology International

This course is general information, not medical advice. If you have ongoing sleep problems, loud snoring with pauses or gasping, or sleepiness that affects driving or work, see your doctor. In Australia, if you are struggling or feel unsafe, call Lifeline on 13 11 14.