OffsetYour body clock is in the wrong place.
Jet lag is a mismatch between your internal day and the local day. Light at the right time can help move that clock. Light at the wrong time can move it the other way.
You landed in London.
Your body is still in Sydney.
The clock on your phone changes at once. Your body takes longer. Offset estimates how sleep and light can move you toward local time while accounting for the sleep the flight may cost you.
What causes jet lag?
Jet lag follows rapid travel across time zones when the body clock remains aligned with the old light and sleep pattern. The local day changes immediately, but sleep, alertness and other daily rhythms take time to move. Sleep lost during the trip can make the same period feel harder.
One trip can create two different problems.
You may also be short on sleep.
Travel fatigue and jet lag can happen together. Rest can reduce the burden of lost sleep even when that sleep does not move the body clock.
This distinction follows the 2021 review and consensus on travel fatigue and jet lag.
With light, when changes the effect.
Light is one of the main signals that keeps the body clock aligned with day and night. Exposure at one part of the body-clock cycle can move timing earlier. Exposure at another part can move it later.
That is why “get morning light” is not a complete jet lag plan. Direction, size of the shift, usual sleep and the body clock’s current estimate all change the useful window.
The scientifically useful time still has to fit on the flight.
A phase window can overlap with takeoff, landing or a connection. Offset treats those as limits on the plan rather than asking the traveler to solve the conflict.
SYDNEYSleep later before departure
SYD → SINUse the cabin sleep that fits
SINGAPOREStay awake for the connection
LONDONContinue after arrival
Each part of the plan has a different job.
Help move the body clock.
Offset places periods to seek or avoid bright light according to the direction and estimated body time.
Meet the need for rest.
Sleep and short naps can address lost sleep. Cabin and connection sleep count for less than sleep on the ground.
Support alertness.
Caffeine can help while you need to stay awake, but taking it too late may work against later sleep.
Optional and sensitive to timing.
Melatonin can affect sleep and body-clock timing. Product quality, medicines and personal health make professional advice important.
What the plan knows, estimates and cannot know.
Your flights, connections, usual sleep, destination and the guidance you choose.
How body time may move and where sleep, light and caffeine can fit around the trip.
Your exact biological phase, whether you will sleep, exact cabin conditions or how you will feel.
The evidence has limits.
Offset uses published timing principles. Offset itself does not have clinical outcome evidence. Real-world jet lag trials remain limited, and the same recommendation will not work identically for every person.
See how the timing becomes a plan- CDC Yellow Book: Jet Lag DisorderClinical overview of strategic sleep, timed light, caffeine and melatonin.
- Managing Travel Fatigue and Jet Lag in Athletes2021 review and expert consensus, including the limits of field evidence.
- Jet lag syndrome: circadian organization and managementReview of the body-clock basis of jet lag and timing-dependent interventions.
- AASM review of circadian rhythm sleep disordersEvidence review covering light, sleep scheduling and melatonin for jet lag.