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Rods and cones
There are two types of photoreceptors in the retina of the vertebrate eye: rods and cones. While rods are responsible for peripherical and night vision (in very high numbers in nocturnal animals), cones are responsible for the visual acuity and for distinguishing colours.
There are three types of cones in the eyes of mammals:
- Red cones, also known as L-cones (maximally sensitive to long-wave light).
- Green cones, also known as M-cones (maximally sensitive to medium-wave light).
- Blue cones, also known as S-cones (maximally sensitive to short-wave light).
The human retina has approximately 120 million rods and 6 million cones.