Light therapy for jet lag: the cheapest free intervention

For jet lag, deliberate light exposure timing produces more circadian shift than the natural rate. The biology is well-mapped and the protocols are simple: see jet-lag-protocols for the broader behavioural protocol. This page focuses on the light-therapy specifics.

The phase-response curve in summary#

Light exposure shifts your internal clock. The direction depends on when in your biological day-night cycle the light arrives:

• Light in late evening / early biological night → phase delay (clock shifts later)
• Light in late biological night / early morning → phase advance (clock shifts earlier)

For jet lag protocols, "early biological morning" means the few hours before your normal wake time. If you usually wake at 7 am London time and you've flown to Bangkok, your biological morning is around 13:00 local Bangkok time.

Eastward (advance) strategies#

Eastward travel requires advancing your clock, going to bed earlier than feels natural at the destination.

• Get bright light at the destination from local mid-morning onwards on arrival
• Avoid bright light in the local evening for the first few days (this would be the wrong direction)
• Avoid evening screens more aggressively than usual for the first 3–4 nights
• A light box or wearable light glasses in the morning at the destination can accelerate adjustment

Westward (delay) strategies#

Westward travel requires delaying your clock, staying up later than feels natural.

• Stay up in evening light at the destination
• Avoid bright morning light at the destination on day 1 (this would advance, the wrong direction)
• Black-out curtains in the morning of arrival
• A light box in the late afternoon / early evening can help maintain alertness without misdirecting the shift

How big is the effect#

The natural circadian adjustment rate is roughly 1 hour per day in the right direction. Aggressive light timing can roughly double this in the first 3–4 days. So a 6-hour eastward shift might take 6 days naturally vs. 3–4 days with deliberate light timing.

The trial evidence is modest in size but consistent in direction.

What devices help#

• Outdoor sunlight at the destination is the strongest free intervention. Always the first choice.
• 10,000-lux SAD light boxes are well-evidenced for circadian work; portable for travel but bulky
• Light therapy glasses (Luminette, AYO) are convenient for travel; smaller evidence base
• Bright phone screens are far too dim and small to substitute for any of the above

What about melatonin#

Melatonin has reasonable evidence for jet lag and works synergistically with light timing. It's a POM in the UK: see melatonin-uk-regulatory. For frequent long-haul travellers, discussing prescription melatonin with a GP is reasonable.

A practical eastward protocol (UK → Bangkok, +6 hours)#

Pre-departure days:

• Start shifting bedtime 30–60 minutes earlier per night in the 2–3 days before
• Morning bright light at home

Day of arrival (likely landing in the morning):

• Outdoor light from local mid-morning onwards
• Avoid napping more than 20 minutes
• Local bedtime even if not very sleepy

Days 1–3:

• Outdoor light immediately on waking in Bangkok
• Bright environment through the morning
• Minimise light from local mid-evening onwards
• Caffeine in the local morning only

Day 4+:

• Resume normal patterns; you'll be mostly adjusted

What we'd actually say#

Light timing is the cheapest jet lag intervention with the strongest evidence. It costs nothing if you can get outdoors, costs a SAD lamp or glasses if you can't.

The direction is the critical decision. Eastward = morning light at destination. Westward = late afternoon / early evening light at destination. Getting this backwards makes jet lag worse.

For occasional 1–3 zone trips, you'll adjust naturally in 1–3 days regardless. For 6+ zones, deliberate light timing makes a meaningful difference.

When to talk to a clinician#

• Frequent long-haul travel: occupational health input may be useful
• New-onset cardiovascular symptoms in older travellers
• Persistent insomnia or daytime sleepiness lasting weeks after arrival: may not be jet lag
• Discussing prescription melatonin for repeated long-haul travel