How to Use Light to Reduce Jet Lag: Timing, Pre-Flight Shifting and What the Evidence Shows
How light timing shifts the body clock earlier or later, the temperature-minimum rule of thumb, pre-flight shifting studies, and why real-world jet lag trials have mostly been disappointing.
Light can shift the body clock, but timing decides the direction. Light before your body temperature low point delays the clock, and light after it advances it, according to lab phase-response studies. Pre-flight shifting with bright morning light worked in lab studies. Real-world jet lag trials have been mostly disappointing, so treat any protocol as a reasonable plan rather than a proven cure.
This page summarizes research for general information. It is not medical advice. People with eye conditions, bipolar disorder, or who take light-sensitizing medicines should talk to a clinician before using a light box. Melatonin is a medicine in many countries; ask a clinician before using it.
The rule: light before vs after the temperature low point
A laboratory study of 21 adults (Khalsa et al., 2003) mapped how bright light shifts the clock at different times. Phase delays occurred when light was centred before the core body temperature minimum and advances when it came after; at the minimum itself there was no shift. There was no long dead zone during the day.
A popular rule of thumb from the Huberman Lab jet lag episode places the temperature minimum about 90 minutes to 2 hours before your usual wake time, and suggests light in the roughly 4 hours after it to shift earlier, or in the hours before it to shift later. That is a practical estimate, not a measured value for you.
| Direction of travel | Clock needs to | Seek light | Avoid light |
|---|---|---|---|
| East (e.g. US to Europe) | Shift earlier | After your home-time temperature low point | In the hours before it |
| West (e.g. Europe to US) | Shift later | In the local evening | In the early morning, after your low point |
The catch is that your low point stays on home time when you land. After a big eastward jump it can fall in the destination’s morning, so bright light early in the local morning can push the clock the wrong way. The 2022 expert consensus supports the general pattern of bright days and dim evenings once you are adapting.
Where is your temperature low point?
Every light plan depends on this estimate, and sources differ.
| Source | Estimate of the temperature minimum |
|---|---|
| Eastman & Burgess, 2009 | Roughly 3 to 4.5 h before waking, assuming 8 h of sleep |
| CDC Yellow Book | Approximately 2–4 hours before habitual wake time |
| Huberman Lab | About 90 minutes to 2 hours before your average wake time |
The research-based estimates sit earlier than the podcast rule of thumb. If you sleep 23:00 to 07:00, the published figures put your low point roughly between 02:30 and 05:00 home time. When in doubt, the safer move is to delay bright light a little rather than start it too early.
Why east is harder than west
The CDC Yellow Book explains that the internal day of most people runs slightly longer than 24 hours, so delaying is easier than advancing. It gives average adaptation rates of about 1.5 hours per day after westward travel and 1 hour per day after eastward travel.
Big eastward jumps carry an extra risk. Eastman and Burgess note that re-entrainment in the wrong direction is common after eastward travel, especially when 8 or more time zones are crossed. Bright light before your low point can push the clock later instead of earlier. That is why the timing of light matters more than its amount.
Shifting before you fly
Most of the strongest data come from shifting at home before an eastward trip.
| Study | Who | Protocol | Result |
|---|---|---|---|
| Burgess et al., 2003 | 28 young adults | Sleep moved 1 h earlier per day for 3 days, with continuous bright light, intermittent bright light (> 3,000 lux) or dim light (< 60 lux) for 3.5 h after waking | Clock advanced 2.1 h (continuous), 1.5 h (intermittent), 0.6 h (dim) |
| Crowley & Eastman, 2015 | 50 adults | Sleep 1 h earlier per day for 3 days, afternoon melatonin, ~5,000 lux light box in 3 patterns | 2 h of light: 2.4 h advance; a single 30-min exposure gave 75% of that |
| Smith et al., 2009 | 22 young adults | 2-h bright light on waking, blue-enriched vs white | No significant difference (92 vs 76 min) |
The 2009 study concluded that blue-enriched light “is no more effective than standard bright light therapy for phase advancing circadian rhythms at commonly used therapeutic light levels.” Burgess and colleagues noted that a 2-hour head start may seem small against a 6 to 9 hour time change, but it reduces how far the clock must shift after arrival.
A worked plan from published models
Eastman and Burgess (2009) built day-by-day plans from lab phase-response data. The table condenses their principles; it is a planning template, not a tested prescription.
| Step | Flying west (clock must shift later) | Flying east (clock must shift earlier) |
|---|---|---|
| 2–3 days before | Go to bed and wake later; bright light in the evening before sleep | Go to bed and wake about 1 h earlier per day; bright light soon after waking |
| Light to avoid | Bright light after waking, until your low point has moved later | Bright light before your low point, which can fall in the local early morning |
| Darkness tools | Very dark sunglasses outdoors in the morning; dark bedroom | Very dark sunglasses or staying indoors in the local early morning; dark bedroom |
| After landing | Light in the local late afternoon and evening | Light in the later morning and around midday, moving earlier each day |
| Expected pace | About 1.5 h per day | About 1 h per day |
In their westward example, a light box in the 2 h before sleep on the two nights before the flight moved the traveller’s low point from 4:00 to about 8:00 am, after which they avoided light after waking. For advancing, they recommend shifting sleep no more than 1 h per day, and only about half an hour per day for night owls, because faster schedules did not shift the clock significantly more.
Other timing tools
- Short trips: the CDC suggests staying on home time for trips of less than about 2 days.
- Naps: short naps of 20–30 minutes can help alertness, while longer daytime naps may disturb night sleep.
- Melatonin: the CDC notes that 0.5–1 mg is often sufficient to shift the clock, advises against high doses (>5 mg), and warns that US products are not regulated by the FDA, so the dose may differ from the label. Timing matters as much as for light, so ask a clinician or pharmacist first.
What happens in real travel
A 2019 systematic review (Bin et al.) looked at 13 controlled studies of people actually flying across time zones, using light, exercise, diet and other strategies. “Nine studies found no significant change in the outcomes, three reported mixed findings, and one was positive.” The authors blamed poorly designed circadian interventions and the neglect of travel fatigue, and called for studies that schedule darkness as well as light before, during and after the flight.
So the lab logic is sound, but evidence that it reliably prevents jet lag symptoms is thin.
Practical plan consistent with the evidence
- Before an eastward trip: if your schedule allows, move bedtime and wake time earlier by about an hour a day for a few days and get bright light soon after waking, as in the pre-flight studies.
- After landing east: avoid bright light in the hours before your home-time temperature low point, and get outdoor light later in the morning and around midday.
- After landing west: get light in the local late afternoon and evening, and keep early-morning light low for the first days.
- Darkness counts too: an eye mask and sunglasses at the wrong times are as much a part of the plan as light. The evening clock is sensitive: Zeitzer et al. found about 100 lux produced half the effect of about 9,000 lux.
Related: morning sunlight protocol, shift work light protocol and the light and circadian rhythm guide.
FAQ
- Should I get morning or evening light after flying east?
- Morning light, but not too early. Flying east you need to shift your clock earlier, which light after your body's temperature low point does. Right after a big eastward jump that low point can fall in the destination's morning, so light very early in the local morning can push the clock the wrong way.
- How many days does it take to adjust to a new time zone?
- The CDC gives average adaptation rates of about 1 hour per day after flying east and about 1.5 hours per day after flying west. A 6-hour eastward trip can therefore take most of a week without help.
- Why is flying east harder than flying west?
- Most people's internal day runs slightly longer than 24 hours, so shifting later is easier than shifting earlier. After eastward flights across 8 or more time zones, the clock often shifts the wrong way round the dial instead.
- What is the temperature minimum and when is mine?
- It is the lowest point of core body temperature, and the crossover point where light switches from delaying to advancing the clock. Published estimates put it about 2 to 4.5 hours before your usual wake time; a popular podcast rule of thumb puts it closer to wake time.
- Should I adjust for a short trip?
- For trips of less than about 2 days, CDC guidance suggests keeping sleep, activity and meals on home time rather than trying to adapt.
- Can I adjust before I travel?
- Lab studies suggest yes. Shifting sleep 1 hour earlier per day for 3 days with bright morning light advanced the clock by about 1.5 to 2.4 hours.
- Do blue-light boxes work better than white ones?
- Not in the one study that compared them: blue-enriched and standard bright white light gave similar phase advances.
- Is there proof these protocols prevent jet lag?
- Not strong proof. A 2019 review of 13 real-travel studies found that 9 showed no significant effect, which the authors attributed partly to poorly designed light and dark schedules.
Sources
- Paper What works for jetlag? A systematic review of non-pharmacological interventions Systematic review, 13 controlled studies of real air travel (Bin et al., Sleep Med Rev, 2019)
- Paper A phase response curve to single bright light pulses in human subjects Laboratory study, 21 adults (Khalsa et al., 2003)
- Paper Preflight Adjustment to Eastward Travel: 3 Days of Advancing Sleep with and without Morning Bright Light Study of 28 young adults, 3 treatment groups (Burgess et al., J Biol Rhythms, 2003)
- Paper Phase advancing human circadian rhythms with morning bright light, afternoon melatonin, and gradually shifted sleep: can we reduce morning bright-light duration? Laboratory study, 50 adults, 3 light patterns plus afternoon melatonin (Crowley & Eastman, Sleep Med, 2015)
- Paper Phase advancing the human circadian clock with blue-enriched polychromatic light Laboratory study, 22 young adults, blue-enriched vs white light (Smith, Revell & Eastman, Sleep Med, 2009)
- Paper Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression Laboratory dose-response study, 23 adults (Zeitzer et al., 2000)
- Paper Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults International expert consensus recommendations (Brown et al., PLOS Biology, 2022)
- Paper How to Travel the World Without Jet Lag Review with worked light, dark and melatonin travel plans (Eastman & Burgess, Sleep Med Clin, 2009)
- Source Jet Lag Disorder (CDC Yellow Book 2026) CDC clinical travel guidance (Riedy & Williams, 2025)
- Episode Find Your Temperature Minimum to Defeat Jetlag, Shift Work & Sleeplessness Huberman Lab, 2021; source of the temperature-minimum rule of thumb