Rods and cones enable visual perception, i.e. vision. The light-sensitive rods let us see differences in brightness even at night
The special features of night vision are:
- The disappearance of colors
- The low visual acuity
- The better visibility of faint objects in the periphery of the field of view
Cones on the other hand serve to perceive colors and require more light. In darkness, humans perceive no colors but only shades of grey. It is only with increasing luminance that the eye switches from night vision (scotopic vision) via twilight vision (mesopic vision) to colored daytime vision (photopic vision) .
This distinguishes the cone system:
- A low sensitivity to light
- Concentration mainly in the central area around the fovea
- Perception of colors and high visual acuity when looking at objects that are fixed, i.e. whose image falls into the fovea
The photosensitive ganglion cells represent a special type of photoreceptor. They have only been analyzed more closely since the 1990s. They are not used for seeing like the other two receptors, but use brightness information to control e.g. the circadian rhythm, the "internal clock" of humans during the day and night.