Color vision rides on about 6 million cones — night vision on 120 million rods
Two kinds of light-sensing cells split the work: a vast army for the dark, a smaller squad for color and detail.
The human retina is paved with two types of light-sensing cells. Rods handle dim light: there are on the order of 120 million of them, and they let you find your way by starlight — but they are colour-blind. Cones, numbering roughly 6 million, work in bright light and deliver both colour and fine detail.
Colour vision comes from just three kinds of cone, tuned to long (red), medium (green) and short (blue) wavelengths. Every hue you perceive is the brain’s reading of how strongly each of the three is firing.
The cones are not spread evenly. They crowd into the fovea, a tiny central pit that is your zone of sharpest sight; its very centre is entirely rod-free. That is why a faint star vanishes when you stare straight at it but reappears when you look slightly to the side — you are sliding its light off the cone-packed centre and onto the more sensitive rods.
Sources & references
2 referencesWell-established. Corroborated by 2 independent sources.
