Light, the first lever against jet lag

Specialized cells in the retina, rich in melanopsin, capture light and directly inform the central clock in the brain. This is the signal that resets it every day.

The effect of light depends on the biological time at which it is received. The reference point is the minimum body temperature, which usually occurs 2 to 3 hours before your usual wake-up time.

• Received in the hours after that point, light advances the clock: useful when flying east.
• Received in the hours before it, light delays it: useful when flying west.

After a long flight, your “biological morning” can fall in the middle of the local afternoon. That is why generic advice like “go out in the morning” can, in some cases, slow down adaptation.

Outdoor daylight is much more intense than indoor lighting, even on an overcast day. When you need to seek light, going outside is therefore the best option. When you need to avoid it, sunglasses are often enough.