Fluorescence micrograph of a section through retina of human eye showing arrangement of rods & cones (photosensitive cells). Cones appear as large, green cells (some appear yellow) & the rods as smaller units in more regular arrangement. Rods outnumber cones 18/20:1. Cones contain a photosensitive chemical iodopsin & are associated with daylight & colour vision. Rods contain rhodopsin (visual purple), a light-sensitive pigment which breaks down in bright light, & are receptors for night or low-light vision. Photo from Guigoz film insNaissance du cerveau dix milliards de galaxiesins by Claude Edelmann.