Editing Color vision (section)

==Wavelength==
{{Spectral colors simple table}}
[[Isaac Newton]] discovered that [[Electromagnetic spectrum#Visible radiation (light)|white light]] after being split into its component colors when passed through a [[dispersive prism]] could be recombined to make white light by passing them through a different prism.[[File:Eyesensitivity.svg|thumb|upright=1.25|[[Photopic]] relative brightness sensitivity of the human visual system as a function of wavelength ([[luminosity function]])]] The [[Visible spectrum|visible light spectrum]] ranges from about 380 to 740 nanometers. [[Spectral color]]s (colors that are produced by a narrow band of wavelengths) such as red, orange, yellow, green, cyan, blue, and violet can be found in this range. These spectral colors do not refer to a single wavelength, but rather to a set of wavelengths: red, 625–740&nbsp;nm; orange, 590–625&nbsp;nm; yellow, 565–590&nbsp;nm; green, 500–565&nbsp;nm; cyan, 485–500&nbsp;nm; blue, 450–485&nbsp;nm; violet, 380–450&nbsp;nm.

Wavelengths longer or shorter than this range are called [[infrared]] or [[ultraviolet]], respectively. Humans cannot generally see these wavelengths, but other animals may.

=== Hue detection ===
Sufficient differences in wavelength cause a difference in the perceived [[hue]]; the [[just-noticeable difference]] in wavelength varies from about 1&nbsp;[[nanometer|nm]] in the [[blue-green]] and [[yellow]] wavelengths to 10&nbsp;nm and more in the longer red and shorter blue wavelengths. Although the human eye can distinguish up to a few hundred hues, when those pure [[spectral color]]s are mixed together or diluted with white light, the number of distinguishable [[chromaticity|chromaticities]] can be much higher.

In very low light levels, vision is [[scotopic]]: light is detected by [[rod cell]]s of the [[retina]]. Rods are maximally sensitive to wavelengths near 500&nbsp;nm and play little, if any, role in color vision. In brighter light, such as daylight, vision is [[photopic]]: light is detected by [[cone cell]]s which are responsible for color vision. Cones are sensitive to a range of wavelengths, but are most sensitive to wavelengths near 555&nbsp;nm. Between these regions, [[mesopic vision]] comes into play and both rods and cones provide signals to the [[retinal ganglion cell]]s. The shift in color perception from dim light to daylight gives rise to differences known as the [[Purkinje effect]].

The perception of "white" is formed by the entire spectrum of visible light, or by mixing colors of just a few wavelengths in animals with few types of color receptors. In humans, white light can be perceived by combining wavelengths such as red, green, and blue, or just a pair of [[complementary color]]s such as blue and yellow.<ref>{{cite encyclopedia | vauthors = Davson H, Perkins ES | title = Human eye | url = https://www.britannica.com/science/human-eye | encyclopedia = Encyclopedia Britannica | date = 7 August 2020 }}</ref>

=== Non-spectral colors ===
There are a variety of colors in addition to spectral colors and their hues. These include [[Greyscale|grayscale colors]], shades of colors obtained by mixing grayscale colors with spectral colors, violet-red colors, [[impossible color]]s, and [[metallic color]]s.

Grayscale colors include white, gray, and black. Rods contain rhodopsin, which reacts to light intensity, providing grayscale coloring.

Shades include colors such as pink or brown. Pink is obtained from mixing red and white. Brown may be obtained from mixing orange with gray or black. Navy is obtained from mixing blue and black.

Violet-red colors include hues and shades of magenta. The light spectrum is a line on which violet is one end and the other is red, and yet we see hues of purple that connect those two colors.

Impossible colors are a combination of cone responses that cannot be naturally produced. For example, medium cones cannot be activated completely on their own; if they were, we would see a 'hyper-green' color.