How to reset your circadian rhythm: a 5-step light plan

To reset your circadian rhythm, keep one wake time every day, get bright outdoor light within 2 hours of waking, and dim your lights for 3 hours before bed. Shift no more than about 1 hour a day. In studies, brighter mornings and darker evenings moved the clock about 2 hours earlier in 3 to 7 days.¹²

What resetting your circadian rhythm actually means

Your master clock sits in the brain and runs on a cycle that averages 24.18 hours, a little longer than a day.³ Without a daily correction, it drifts later. Light is the main correction. Bright light in the hours before your body’s temperature low (roughly 2 to 3 hours before you normally wake) pushes the clock later, and light after that low pulls it earlier.⁴⁵

Researchers track the clock by when melatonin starts rising in the evening. “Resetting” means moving that time, and sleepiness moves with it. Most people want to go earlier, which is the harder direction: the clock delays more easily than it advances.⁴

How to reset your circadian rhythm in 5 steps

1. Fix your wake time, 7 days a week

Anchor the wake time, not the bedtime. You can set an alarm for 7 a.m., but you cannot force sleep at 10 p.m., and your wake time decides when your morning light arrives.

Irregular schedules go with late clocks. In 61 undergraduates tracked for 30 days, the least regular fifth had a melatonin onset around 12:08 a.m., against 9:32 p.m. for the most regular fifth, more than 2.5 hours later. A model of their data pinned most of the gap on their different light patterns.⁶ This was an observational study, so it shows a link, not proof.

Weekends matter. In a Colorado study, 5 people who spent an ordinary weekend at home came back with melatonin onset 0.98 hours later than before it.⁷ If dark mornings make a fixed alarm hard, a sunrise alarm clock is one option.

2. Get bright light in the first 2 hours

This is the step that does the most work. In a trial of 28 adults, everyone moved their sleep 1 hour earlier each day for 3 days. The group kept in dim indoor light (under 60 lux) shifted 0.6 hours. Groups that sat in bright light above 3,000 lux for the first 3.5 hours after waking shifted 1.5 hours (light on and off every 30 minutes) and 2.1 hours (continuous).²

Indoor light rarely gets close. Typical room lighting is about 200 lux, and studies commonly use 1,000 lux as the cutoff for outdoor light.¹ An expert panel recommends at least 250 lux melanopic equivalent daylight illuminance at eye level throughout the day, with daylight as the first source.⁸

In practice: go outside within an hour or two of getting up, and stay out as long as your morning allows. Walk, eat breakfast outside, or commute on foot. The light exposure planner shows your local sunrise, and the morning sunlight guide has more on getting enough.

Time it after your usual wake time, not hours before it. Light that lands before your temperature low can push a late clock even later.⁵

When mornings are dark, a light box is the fallback. A meta-analysis of 53 studies (1,154 participants) found light therapy helped circadian rhythm sleep disorders with a small-to-medium effect (Hedges’ g 0.41). The effect was smaller in randomized trials, and there were signs of publication bias.⁹ See our light therapy lamps for models and specs.

3. Dim the last 3 hours before bed

The same expert panel set a ceiling of 10 lux melanopic for the evening, starting at least 3 hours before bed, and under 1 lux in the bedroom. Warm white LEDs at 2,700 to 3,000 K meet the evening target at about 30 lux.⁸

The clock responds to ordinary room light. In 55 young adults, half of the evening melatonin signal was suppressed at about 25 lux, and individual sensitivity ranged from 6 lux to 350 lux. Five hours at 30 lux pushed the melatonin rise back by 77 minutes.¹⁰

Screens add to it. In 12 adults who read on a light-emitting eReader for about 4 hours before bed for 5 nights, melatonin onset came more than 1.5 hours later than with a printed book, and they took about 10 minutes longer to fall asleep.¹¹

Use low, warm lamps in the evening, such as amber or dimmable circadian bulbs, and turn screen brightness down. Block streetlight and early summer sun with blackout curtains so the bedroom stays dark.

4. Time caffeine, exercise and meals

These are smaller levers than light, but they can add to your progress or undo it.

• Caffeine. In a placebo-controlled study of 5 adults, a dose equal to a double espresso (about 200 mg for a 69 kg person) taken 3 hours before bed delayed the melatonin rhythm by about 40 minutes. That was close to half the delay from 3 hours of bright light at bedtime.¹² The caffeine cutoff calculator works out a last-cup time.
• Exercise. In 99 adults in a lab study, 1 hour of moderate treadmill exercise on 3 days at 7 a.m. or between 1 and 4 p.m. shifted the clock earlier, while exercise from 7 to 10 p.m. shifted it later.¹³
• Meals. When 10 men ate all meals 5 hours later for 6 days, melatonin and cortisol rhythms did not move. Their blood sugar rhythm shifted 5.7 hours and a clock gene in fat tissue shifted about 1 hour.¹⁴ Meals set the clocks in your organs more than the master clock, so eat at regular times that match your new schedule.

5. Move no more than 1 hour a day

A faster schedule does not mean a faster clock. In 26 adults given bright morning light, one group moved sleep 1 hour earlier a day and another 2 hours earlier a day, for 3 days. The clock advanced a median 1.4 and 1.9 hours, a difference that was not significant. By day 3, the 2-hour group had trouble falling asleep because sleep had outrun the clock.¹⁵

So about 1 hour a day is the practical limit for your schedule, and the clock still lags behind it. Even with bright light, 3 days of 1-hour steps moved it 1.4 to 2.1 hours, and in dim light about 12 minutes a day.²¹⁵ To move 3 hours earlier, plan on most of a week with strong morning light, and longer without.

How fast can you reset your circadian rhythm?

Results from the studies above, all measured by melatonin timing:

What people did	People	Clock shift
A summer week camping with only natural light	8	About 2 h earlier1
A winter week camping with only natural light	5	About 2.6 h earlier7
A summer weekend camping	9	1.4 h earlier7
An ordinary weekend at home	5	0.98 h later7
Sleep 1 h earlier a day for 3 days, dim indoor light	28 in 3 groups	0.6 h earlier2
Same, plus 3.5 h of bright light after waking	28 in 3 groups	1.5 to 2.1 h earlier2
Reading a light-emitting eReader about 4 h before bed, 5 nights	12	More than 1.5 h later11
Double-espresso dose of caffeine 3 h before bed	5	About 40 min later12
All meals 5 h later for 6 days	10	No change in melatonin14

Travel data tell the same story. Early estimates from real travelers put adjustment at about 57 minutes a day after flying east and 92 minutes a day after flying west.⁴ Our jet lag guide applies this to trips.

What camping studies show about a circadian rhythm reset

The best-known evidence comes from two small camping studies in the Colorado Rockies.

In the first, 8 adults spent a July week with no electric light, not even flashlights. Their daytime light exposure rose more than fourfold, from 979 to 4,487 lux on average, and they got 3,074 lux in the first 2 hours after waking against 934 lux at home. Evening light between sunset and sleep fell from 21 to 8 lux.

All melatonin markers moved about 2 hours earlier, so melatonin started near sunset. Later chronotypes shifted the most.¹

The follow-up ran in winter and on a weekend. Five people who camped for a week near the winter solstice got more than 13 times their usual daytime light (10,297 vs 752 lux), and their melatonin onset moved about 2.6 hours earlier. A weekend was enough for most of the effect: 9 summer campers shifted 1.4 hours earlier, about 69% of the shift the earlier study saw after a full week, while 5 people who stayed home drifted 0.98 hours later.⁷

The tent was not the active ingredient. Brighter days and dimmer evenings were. You can copy most of that at home with morning time outdoors, a dim evening and a dark bedroom. If you want to know how late your clock runs before you start, the chronotype quiz below estimates it from your free-day sleep.

How to keep your clock from drifting back

• Keep the wake time after the reset. A home weekend moved the clock about an hour later in one study.⁷
• Keep getting morning light. The same 3-day schedule change moved the clock 0.6 hours in dim light, against 1.5 to 2.1 hours with bright light.²
• Watch late screens and caffeine. Both delayed the clock in controlled studies.¹¹¹²

Relapse is common even after treatment that works. A 2016 review of delayed sleep phase disorder notes frequent relapse at follow-up.¹⁶

When to see a doctor: delayed sleep-wake phase disorder

Some late sleepers have a disorder, not a habit. Delayed sleep-wake phase disorder (DSWPD) means your sleep and wake times are habitually delayed, usually by more than 2 hours, compared with conventional times.

People with it cannot fall asleep earlier on work or school nights and struggle to get up. Symptoms must last at least 3 months, and diagnosis needs at least 7 days of sleep diary or wrist actigraphy.¹⁷ It is the most commonly diagnosed circadian sleep disorder and mostly affects teenagers and young adults.¹⁶

The treatment evidence is modest. The American Academy of Sleep Medicine’s 2015 guideline gave a weak recommendation for light after waking combined with behavioral treatment in children and adolescents with DSWPD, and found too little evidence to recommend light therapy on its own.¹⁷ A sleep physician can confirm the diagnosis and discuss other timed treatments.

See a doctor if:

• Your sleep times fit the DSWPD pattern above.
• Two to three weeks of a fixed wake time, morning light and dim evenings have not moved you.
• You are very sleepy in the day even when you get enough hours.
• Your sleep changed along with your mood.

Be careful with bright light if you have bipolar disorder. In a review of 799 people with bipolar depression treated with light, 0.9% switched into mania and 1.4% into hypomania. When rating scales were used the rate was 3%, close to the roughly 4% expected on placebo. Among the 16 people with rapid cycling it was 18.8%.¹⁸

Talk to your psychiatrist before using a light box. People with eye disease or who take medicines that make the eyes sensitive to light may need an eye doctor’s clearance before light therapy.¹⁹

Footnotes

1. Wright KP Jr, McHill AW, Birks BR, et al. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol. 2013;23(16):1554-1558. doi:10.1016/j.cub.2013.06.039 ↩ ↩² ↩³ ↩⁴

2. Burgess HJ, Crowley SJ, Gazda CJ, et al. Preflight adjustment to eastward travel: 3 days of advancing sleep with and without morning bright light. J Biol Rhythms. 2003;18(4):318-328. doi:10.1177/0748730403253585 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

3. Czeisler CA, Duffy JF, Shanahan TL, et al. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science. 1999;284(5423):2177-2181. doi:10.1126/science.284.5423.2177 ↩

4. Eastman CI, Burgess HJ. How to travel the world without jet lag. Sleep Med Clin. 2009;4(2):241-255. doi:10.1016/j.jsmc.2009.02.006 ↩ ↩² ↩³

5. Khalsa SB, Jewett ME, Cajochen C, Czeisler CA. A phase response curve to single bright light pulses in human subjects. J Physiol. 2003;549(Pt 3):945-952. doi:10.1113/jphysiol.2003.040477 ↩ ↩²

6. Phillips AJK, Clerx WM, O’Brien CS, et al. Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing. Sci Rep. 2017;7(1):3216. doi:10.1038/s41598-017-03171-4 ↩

7. Stothard ER, McHill AW, Depner CM, et al. Circadian entrainment to the natural light-dark cycle across seasons and the weekend. Curr Biol. 2017;27(4):508-513. doi:10.1016/j.cub.2016.12.041 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

8. Brown TM, Brainard GC, Cajochen C, 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. doi:10.1371/journal.pbio.3001571 ↩ ↩²

9. van Maanen A, Meijer AM, van der Heijden KB, Oort FJ. The effects of light therapy on sleep problems: a systematic review and meta-analysis. Sleep Med Rev. 2016;29:52-62. doi:10.1016/j.smrv.2015.08.009 ↩

10. Phillips AJK, Vidafar P, Burns AC, et al. High sensitivity and interindividual variability in the response of the human circadian system to evening light. Proc Natl Acad Sci U S A. 2019;116(24):12019-12024. doi:10.1073/pnas.1901824116 ↩

11. Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A. 2015;112(4):1232-1237. doi:10.1073/pnas.1418490112 ↩ ↩² ↩³

12. Burke TM, Markwald RR, McHill AW, et al. Effects of caffeine on the human circadian clock in vivo and in vitro. Sci Transl Med. 2015;7(305):305ra146. doi:10.1126/scitranslmed.aac5125 ↩ ↩² ↩³

13. Youngstedt SD, Elliott JA, Kripke DF. Human circadian phase-response curves for exercise. J Physiol. 2019;597(8):2253-2268. doi:10.1113/JP276943 ↩

14. Wehrens SMT, Christou S, Isherwood C, et al. Meal timing regulates the human circadian system. Curr Biol. 2017;27(12):1768-1775.e3. doi:10.1016/j.cub.2017.04.059 ↩ ↩²

15. Eastman CI, Gazda CJ, Burgess HJ, et al. Advancing circadian rhythms before eastward flight: a strategy to prevent or reduce jet lag. Sleep. 2005;28(1):33-44. doi:10.1093/sleep/28.1.33 ↩ ↩²

16. Micic G, Lovato N, Gradisar M, et al. The etiology of delayed sleep phase disorder. Sleep Med Rev. 2016;27:29-38. doi:10.1016/j.smrv.2015.06.004 ↩ ↩²

17. Auger RR, Burgess HJ, Emens JS, et al. Clinical practice guideline for the treatment of intrinsic circadian rhythm sleep-wake disorders: an update for 2015. J Clin Sleep Med. 2015;11(10):1199-1236. doi:10.5664/jcsm.5100 ↩ ↩²

18. Benedetti F. Rate of switch from bipolar depression into mania after morning light therapy: a historical review. Psychiatry Res. 2018;261:351-356. doi:10.1016/j.psychres.2018.01.013 ↩

19. Galima SV, Vogel SR, Kowalski AW. Seasonal affective disorder: common questions and answers. Am Fam Physician. 2020;102(11):668-672. aafp.org ↩