The colors of the visible light spectrum.
color wavelength interval frequency interval
red ~ 625-740 nm ~ 480-405 THz
orange ~ 590-625 nm ~ 510-480 THz
yellow ~ 565-590 nm ~ 530-510 THz
green ~ 500-565 nm ~ 600-530 THz
cyan ~ 485-500 nm ~ 620-600 THz
blue ~ 440-485 nm ~ 680-620 THz
violet ~ 380-440 nm ~ 790-680 THz
Continuous optical spectrum
Designed for monitors with gamma 1.5.
The bars below show the relative intensities of the three
colors mixed to make the color immediately above.
Color, frequency, and energy of light.
Color /nm /1014 Hz /104 cm-1 /eV /kJ mol-1
Infrared >1000 <3.00 <1.00 <1.24 <120
Red 700 4.28 1.43 1.77 171
Orange 620 4.84 1.61 2.00 193
Yellow 580 5.17 1.72 2.14 206
Green 530 5.66 1.89 2.34 226
Blue 470 6.38 2.13 2.64 254
Violet 420 7.14 2.38 2.95 285
Near ultraviolet 300 10.0 3.33 4.15 400
Far ultraviolet <200 >15.0 >5.00 >6.20 >598
Electromagnetic radiation is a mixture of radiation of different wavelengths
and intensities. When this radiation has a wavelength inside the human
visibility range (approximately from 380 nm to 740 nm), it is called light.
The light's spectrum records each wavelength's intensity. The full spectrum
of the incoming radiation from an object determines the visual appearance
of that object, including its perceived color. As we will see, there are
many more spectra than color sensations; in fact one may formally define
a color to be the whole class of spectra which give rise to the same color
sensation, although any such definition would vary widely among different
species and also somewhat among individuals intraspecifically.
A surface that diffusely reflects all wavelengths equally is perceived
as white, while a dull black surface absorbs all wavelengths and does
not reflect (for mirror reflection this is different: a proper mirror
also reflects all wavelengths equally, but is not perceived as white,
while shiny black objects do reflect).
The familiar colors of the rainbow in the spectrum—named from the
Latin word for appearance or apparition by Isaac Newton in 1671—contains
all those colors that consist of visible light of a single wavelength
only, the pure spectral or monochromatic colors.
The frequencies are approximations and given in terahertz (THz). The
wavelengths, valid in vacuum, are given in nanometers (nm). A list of
other objects of similar size is available.
The color table should not be interpreted as a definite list—the
pure spectral colors form a continuous spectrum, and how it is divided
into distinct colors is a matter of taste and culture; for example, Isaac
Newton identified the seven colors red, orange, yellow, green, blue, indigo,
and violet, remembered by many school children using mnemonics such as
Roy G. Biv, Richard Of York Gave Battle In Vain and VIBGYOR. Similarly,
the intensity of a spectral color may alter its perception considerably;
for example, a low-intensity orange-yellow is brown, and a low-intensity
yellow-green is olive-green.
Spectral versus non-spectral colors
Most light sources are not pure spectral sources; rather they are created
from mixtures of various wavelengths and intensities of light. To the
human eye, however, there is a wide class of mixed-spectrum light that
is perceived the same as a pure spectral color. In the table above, for
instance, when your computer screen is displaying the "orange"
patch, it is not emitting pure light at a fixed wavelength of around 600
nm (which is in fact not a thing most computer screens are even able to
do). Rather, it is emitting a mixture of about two parts red to one part
green light. Were you to print this page on a color printer, the orange
patch on the paper, when lit with white light, would reflect yet another,
more continuous spectrum. We cannot see those differences (although many
animals can), and the reason has to do with the pigments that make up
our color vision cells (see below).
A useful quantification of this property is the dominant wavelength,
which matches a wavelength of spectral light to a non-spectral source
that evokes the same color perception. Dominant wavelength is the formal
background for the popular concept of hue.
In addition to the many light sources that can appear to be pure spectral
colors but are actually mixtures, there are many color perceptions that
by definition cannot be pure spectral colors due to desaturation or because
they are purples (which do not appear in the Newtonian pure spectrum).
Some examples of necessarily non-spectral colors are the achromatic colors
(black, gray and white) and other colors such as pink, tan and magenta.
See metamerism (color) for a basic intro to why color matching challenges
the wave equation
The wave equation describes the behavior of light and so we should be
able to describe color spectra in terms of the mathematical properties
of the solutions of the wave equation. However, to understand which particular
color perception will arise from a particular physical spectrum requires
knowledge of the specific retinal physiology of the observer. For completeness,
we include a simple equation for light traveling in a vacuum:
Main William1 William2 color1 color2 color3 color4 color5glassesArchitecural
where the subscripts denote partial derivatives and c is the speed of
light. If we fix (x,y,z) a point in space and look at the solution u(x,y,z,t)
as a function of t, we obtain a signal. If we take the Fourier transform
of this signal, we obtain a frequency decomposition as described above.
Each frequency has an amplitude and phase. The frequency multiplied by
Planck's constant h determines the energy of a photon of the relevant
component. The square of the amplitude represents the intensity, which
is the amount of energy transmitted per second through a unit area of
a surface perpendicular to the light propagation. The phase information
is much more mysterious because it is difficult to measure and observe.
Humans cannot perceive phase effects of light except in special cases
of interference (e.g. see thin-film optics) where phase effects lead to
perceptible amplitude changes. Most light has randomly distributed phases,
but lasers are more efficient when the photons all have the same phase.
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