bio

Melanopsin

The light-sensitive pigment carried by a scattered population of retinal ganglion cells, which makes those cells directly photosensitive and wires them straight to the master clock in the hypothalamus rather than to the parts of the brain that build images. They are not for seeing - they are a light meter, and it reports to the clock. This is why a mouse with no working rods or cones, visually blind, still entrains perfectly to a light cycle, and why many blind humans do too. Melanopsin peaks in the blue, around 480 nanometres - meaning the *colour* of a light source, not just its brightness, determines how loudly it speaks to the clock.