Every frequent traveller has a strategy for jet lag. Melatonin at the destination bedtime. Staying awake on the plane. Avoiding caffeine. Some people swear by fasting. Almost none of them use light deliberately — which is a shame, because light is the only thing that actually resets the circadian clock rather than just managing symptoms.
Melatonin can help you sleep at the right time. It doesn't shift your clock faster. Exercise can help with fatigue. It doesn't resolve the phase mismatch. Light does both: it directly acts on the suprachiasmatic nucleus to advance or delay the circadian phase, shortening the time to re-entrainment.
Why Direction of Travel Matters
Eastward and westward jet lag are biologically different problems, and they need different solutions.
Travelling east — London to Tokyo, New York to London — means your clock needs to advance: wake up and sleep earlier than your body wants to. This is harder for most people because the circadian clock naturally runs slightly longer than 24 hours. It resists being pushed earlier.
Travelling west — London to New York, Tokyo to London — means your clock needs to delay: wake up and sleep later. This is easier. The clock runs long naturally, so delaying it requires less work.
Rule of thumb: eastward travel causes more severe jet lag. The general estimate is one day of adjustment per time zone crossed for eastward travel, versus slightly less for westward.
The Light Protocol for Eastward Travel
To advance your clock after flying east, you need bright light in the morning at the destination — specifically in the first 90 minutes after your destination's local sunrise. This drives the circadian phase forward, telling your body clock that morning is now earlier than it was.
Get outside in the morning if you can. Outdoor light, even on a cloudy day, delivers sufficient melanopsin stimulus to drive re-entrainment. If you're at a hotel with limited outdoor access, a 480–490nm light source at your desk for 20–30 minutes during the morning window achieves the same effect.
Critically: avoid bright light in the evening for the first two to three days after arrival. Evening light delays the clock — the opposite of what you need when travelling east. Keep hotel rooms dark after 9pm local time.
The Light Protocol for Westward Travel
To delay your clock after flying west, you want evening light at the destination — light exposure in the two to three hours before your destination's local midnight. This pushes the clock later, making it easier to stay awake until a reasonable local bedtime.
Morning light on westward travel is less helpful in the first few days — wait until you're within an hour or two of your target sleep schedule before shifting to morning light sessions.
Why Hotels Should Be Doing This Automatically
The irony of jet lag is that the environment most likely to cause it — the hotel room — is also perfectly positioned to fix it. A hotel room with PMS-integrated lighting that knows where you flew from, calculates your phase displacement, and delivers the appropriate light protocol through the room luminaires each morning would systematically eliminate the jet lag problem for guests.
That's exactly what LightHealth's hotel circadian system does. The room receives your origin timezone from the hotel's property management system at check-in. The protocol runs automatically. You don't touch an app or adjust a panel. The light simply does its job while you sleep and wake.
Learn about the LightHealth hotel system.
LightHealth products are in development. Join the early access list to be first when we launch.
