Light: The Key Zeitgeber

Light, especially sunlight, is the strongest “time giver” (zeitgeber) for circadian rhythms and sleep. Melanopsin-containing retinal ganglion cells detect light and signal the central circadian clock, called the suprachiasmatic nucleus. Bright light in the morning advances your clock, while light at night delays it. Get sunlight/bright light exposure for 2–10 minutes right after waking, and avoid bright lights 1–2 hours before bed for optimal sleep.