How Light Reaches the Clock

Light doesn't set your clock through the part of the eye you read with. A direct pathway, the retinohypothalamic tract, runs straight from your retina to the SCN and resets it.

What that pathway craves is brightness. A bright office sits near 500 lux, but a cloudy morning outdoors still delivers around 10,000 lux — and full sun far more. That gap is why a few minutes outside beats hours under the ceiling lights.