As a rough approximation based on the number of these extra cones, tetrachromats might see 100 million colours. These rare individuals, mostly women, have a genetic mutation granting them an extra, fourth cone cell. Jameson knows what she's talking about, given her work with 'tetrachromats', people who possess apparent superhuman vision. Still, perception of colour is a highly subjective ability that varies from person to person, thus making any hard-and-fast figure difficult to pinpoint. If two infrared photons smack into a retinal cell nearly simultaneously, their energy can combine, converting them from an invisible wavelength of, say, 1000 nanometres to a visible 500 nanometres (a cool green to most eyes).Ī healthy human eye has three types of cone cells, each of which can register about 100 different colour shades, therefore most researchers ballpark the number of colours we can distinguish at around a million. The lens normally blocks ultraviolet light, so without it, people are able to see beyond the visible spectrum and perceive wavelengths up to about 300 nanometres as having a blue-white colour.Ī study in 2014 pointed out that, in a manner of speaking, we all can see infrared photons, too. Aphakia is the lack of a lens, due to surgical removal for cataracts or congenital defects. While most of us are limited to the visible spectrum, people with a condition called aphakia possess ultraviolet vision.

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