The CIE 1931 color space is an often-used model of spectral sensitivities of the three cells of an average human. Such a difference is caused by the different opsins they carry, OPN1LW, OPN1MW, and OPN1SW, respectively, the forms of which affect the absorption of retinaldehyde. The three types have peak wavelengths in the range of 564–580 nm, 534–545 nm, and 420–440 nm, respectively, depending on the individual. The third type responds the most to blue short-wavelength light, peaking at 420 nm, and make up only around 2% of the cones in the human retina. M cones make up about a third of cones in the human eye. The second most common type responds the most to light of yellow to green medium-wavelength, peaking at 530 nm. The majority of the human cones are of the long type. The first responds the most to light of the longer red wavelengths, peaking at about 560 nm. Humans normally have three types of cones, usually designated L, M and S for long, medium and short wavelengths respectively. The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation different individuals will have cones with different color sensitivity.

Being color blind can change this, and there have been some verified reports of people with four types of cones, giving them tetrachromatic vision. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, humans have trichromatic vision. These cones are sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and longer-wavelength light respectively. Each type expresses a different opsin: OPN1SW, OPN1MW, and OPN1LW, respectively. Cones are normally one of three types: S-cones, M-cones and L-cones. They are also able to perceive finer detail and more rapid changes in images because their response times to stimuli are faster than those of rods. Ĭones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration being towards the macula. Conversely, they are absent from the optic disc, contributing to the blind spot. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. Cones function best in relatively bright light, called the photopic region, as opposed to rod cells, which work better in dim light, or the scotopic region. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone cells or cones are photoreceptor cells in the retinas of vertebrates' eyes.

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