Light, Clocks and Sleep: The Discovery of a New Photoreceptor within the Eye Until the late 1990’s it seemed inconceivable to most vision biologists that there could be an unrecognised class of light sensor within the eye. After all, the eye was the best understood part of the central nervous system. One hundred and fifty years of research had explained how we see: Light is detected by the rods and cones of the retina and their responses are assembled into an “image” by inner retinal neurones, followed by advanced visual processing in the brain. This representation of the eye left no room...