A jet lag protocol that actually uses how light works

For the first few days at your destination, seek bright light during its morning if you travelled east, and during its evening if you travelled west — and try to avoid bright light in the opposite window. This single rule, applied consistently, is the core of every evidence-based jet lag protocol.

Why this works

Left entirely alone, the human circadian clock shifts by only about half an hour to an hour a day toward a new time zone. Cross seven time zones flying east, and without any intervention your body is looking at roughly a week of feeling off before it catches up — which is the miserable jet lag experience most travellers are familiar with.

Light is the strongest lever for speeding this up, and its effect depends entirely on timing relative to your body’s internal clock. Light exposure in the hours before your body’s natural low point — roughly the second half of the night, a few hours before your habitual wake time — pushes the clock later (a phase delay). Light exposure in the hours after that low point pushes the clock earlier (a phase advance). The biggest shifts happen with light exposure close to that low point; light farther from it does less.

This translates into a direction, not just a habit. Travelling east means your body needs to shift earlier, so morning light at your destination is the tool — and avoiding bright light in the evening, when it would push you the wrong way, matters just as much. Travelling west means the opposite: your body needs to shift later, so evening light at your destination helps, while bright morning light can actually work against you for the first couple of days. Melatonin can be layered on with the same directional logic — taken in the evening it helps shift the clock earlier (useful for eastward travel), taken in the morning it helps shift it later (useful for westward travel) — though light is considered the primary driver and melatonin the supporting tool, not the other way around.

How to do it

1. Figure out your direction of travel and match it to the rule: east means seek morning light and avoid evening light at your destination; west means seek evening light and avoid morning light, for the first two to four days.
2. If you’re travelling east across many time zones, consider shifting your sleep and light exposure 30–60 minutes earlier for two to three days before departure — a head start makes the destination adjustment shorter.
3. If you use melatonin, keep the dose low — 0.5 to 1mg is generally enough for the circadian-shifting effect — and time it precisely: evening for eastward travel, morning for westward, avoiding your body’s natural high-melatonin window (roughly midnight to 5am your original time) where it’s least effective.
4. For short trips of only a couple of days, consider not trying to adjust at all — staying on something closer to your home schedule, using light and activity timing to bridge the gap, can be more practical than forcing a shift you’ll just have to reverse days later.
5. Combine light and melatonin timing with normal daytime activity and exercise at your destination where possible — movement adds a modest additional shift in the same direction as correctly timed light.

Common mistakes

• Getting the light direction backwards. Bright light at the wrong time doesn’t just fail to help — it can actively shift your clock the wrong way, making adjustment slower.
• Taking a high dose of melatonin, expecting a faster effect. Above about 1–3mg, extra melatonin mostly just stays active longer at the wrong time rather than shifting the clock faster, and can increase next-day grogginess.
• Trying to fully adjust for a two-day trip. For very short stays, partial or no adjustment is often the more practical strategy — ask whether you’ll actually benefit from resetting a clock you’re about to reset back almost immediately.
• Ignoring pre-departure shifting before a long eastward trip. A few days of earlier light and sleep before you fly gives you a head start that reduces how much adjustment is needed on arrival.
• Forgetting sunglasses as a tool. Avoiding light in the “wrong” window matters as much as seeking it in the right one — sunglasses outdoors during the window you’re meant to avoid light is a legitimate part of the protocol, not overkill.

What should change

With correctly timed light (and melatonin, if used), most travellers adjust to a new time zone within two to four days, compared with roughly a day per time zone crossed with no intervention at all — for a long-haul eastward flight, that’s often the difference between the better part of a week feeling foggy and adjusting by the second or third day.

Your next step

Once you’re adjusted, the same fixed-wake-time and morning-light habits that help with jet lag are what keep a stable rhythm going day to day — worth reading if travel disruption is a recurring pattern rather than a one-off trip.