The Young–Helmholtz theory (based on the work of Thomas Young and

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (; ; 31 August 1821 – 8 September 1894; "von" since 1883) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The ...

in the 19th century), also known as the trichromatic theory, is a theory of trichromatic color vision – the manner in which the

visual system The visual system is the physiological basis of visual perception (the ability to perception, detect and process light). The system detects, phototransduction, transduces and interprets information concerning light within the visible range to ...

gives rise to the phenomenological experience of color. In 1802, Young postulated the existence of three types of photoreceptors (now known as

cone cell Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most v ...

s) in the eye, with different but overlapping response to different wavelengths of visible light. Hermann von Helmholtz developed the theory further in 1850: that the three types of cone photoreceptors could be classified as short-preferring ( violet), middle-preferring (

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a com ...

), and long-preferring ( red), according to their response to the wavelengths of light striking the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

. The relative strengths of the signals detected by the three types of cones are interpreted by the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

as a visible color. For instance, yellow light uses different proportions of red and green, but little blue, so any hue depends on a mix of all three cones, for example, a strong red-sensitive, medium green-sensitive, and low blue-sensitive. Moreover, the intensity of colors can be changed without changing their hues, since intensity depends on the frequency of discharge to the brain, as a blue-green can be brightened but retain the same hue. The system is not perfect, as it does not distinguish yellow from a red-green mixture, but can powerfully detect subtle environmental changes. In 1857,

James Clerk Maxwell James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish physicist and mathematician who was responsible for the classical theory of electromagnetic radiation, which was the first theory to describe electricity, magnetism an ...

used the recently developed

linear algebra Linear algebra is the branch of mathematics concerning linear equations such as :a_1x_1+\cdots +a_nx_n=b, linear maps such as :(x_1, \ldots, x_n) \mapsto a_1x_1+\cdots +a_nx_n, and their representations in vector spaces and through matrix (mathemat ...

to offer a mathematical proof of the Young–Helmholtz theory. The existence of cells sensitive to three different wavelength ranges (most sensitive to yellowish green, cyanish-green, and blue – not red, green and blue) was first shown in 1956 by Gunnar Svaetichin. In 1983 it was validated in human retinas in an experiment by Herbert Dartnall, James Bowmaker, and John Mollon, who obtained microspectrophotopic readings of single eye cone cells. Earlier evidence for the theory had been obtained by looking at light reflected from the retinas of living humans, and absorption of light by retinal cells removed from corpses. While Young is often credited as the progenitor of trichromatic color theory, a theory of color vision by George Palmer is mostly analogous to Young's, but precedes it by a quarter century. In his ''Theory of Colors and Vision'' (1777)Palmer, George. 1777. ''Theory of Colors and Vision'', London: Leacroft. and later in his ''Theory of Light'' (1786),Palmer, G. 1786. ''Theorie de la lumiere'', Paris: Hardouin and Gattey. Palmer claims that the retina has 3 classes of particles that selectively absorb red, yellow and blue rays. The unequal motion of these particles evokes color, and the equal motion thereof evokes white. However, Palmer also claimed that light itself is compounded of only three distinct rays: red, yellow and blue, which differs from the modern understanding (and that of Young), that light is a continuous

visible spectrum The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

References

{{DEFAULTSORT:Young-Helmholtz theory Vision Hermann von Helmholtz