Light Exposure as a Zeitgeber: A Practical Playbook for Jet Lag

The brain's master clock synchronizes primarily to light. Right-time light is the biggest free intervention available; wrong-time light slows recovery.

The rule

Light before usual wake time pulls the clock earlier (eastward). Light after usual bedtime pushes the clock later (westward). Mid-day light barely shifts anything.

Eastward

Bright outdoor light in the destination morning. Avoid bright evening light — sunglasses on the walk home from dinner.

Westward

Bright light in late afternoon at destination. Keep the morning of day one dim — curtains closed, soft indoor lights.

When real sun is not available

A 10,000-lux therapy lamp for 20–30 minutes substitutes. Phone screens and overhead office lights are not bright enough to count.