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The visible spectrum is the portion of the
electromagnetic spectrum The electromagnetic spectrum is the range of frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular ...
that is visible to the
human eye The human eye is a sensory organ (biology), organ, part of the sensory nervous system, that reacts to light, visible light and allows humans to use visual information for various purposes including Visual perception, seeing things, Balance (abil ...
.
Electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
in this range of
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...
s is called ''
visible light Light or visible light is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequency, fr ...
'' or simply
light Light or visible light is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequency, fr ...
. A typical
human eye The human eye is a sensory organ (biology), organ, part of the sensory nervous system, that reacts to light, visible light and allows humans to use visual information for various purposes including Visual perception, seeing things, Balance (abil ...
will respond to wavelengths from about 380 to about 750
nanometers 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
. In terms of frequency, this corresponds to a band in the vicinity of 400–790  terahertz. These boundaries are not sharply defined and may vary per individual. Under optimal conditions these limits of human perception can extend to 310 nm (
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
) and 1100 nm (
near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry mom ...
). The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well. The spectrum does not contain all the
color Color (American English) or colour (British English) is the visual perception, visual perceptual Physical property, property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physica ...
s that the human
visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the a ...
can distinguish. '' Unsaturated colors'' such as
pink Pink is the color of Dianthus plumarius, a namesake flower that is a pale tint of red. It was first used as a color name in the late 17th century. According to surveys in Europe and the United States, pink is the color most often associated with ...
, or
purple Purple is any of a variety of color Color (American English) or colour (British English) is the visual perception, visual perceptual Physical property, property deriving from the spectrum of light interacting with the photoreceptor cel ...
variations like
magenta Magenta () is a color that is variously defined as pinkish- purplish- red, reddish-purplish-pink or mauvish- crimson. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located exactly midway between red and b ...
, for example, are absent because they can only be made from a mix of multiple wavelengths. Colors containing only one wavelength are also called ''pure colors'' or spectral colors. Visible wavelengths pass largely unattenuated through the
Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Gravity of Earth, Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating Atmo ...
via the "
optical window The optical window is a range of wavelengths that are not blocked by the Earth, earth's atmosphere. The window runs from around 300 nanometers (Ultraviolet, ultraviolet-B) up into the range the human eye can detect, roughly 400–700 nm and conti ...
" region of the electromagnetic spectrum. An example of this phenomenon is when clean air scatters blue light more than red light, and so the midday sky appears blue (apart from the area around the sun which appears white because the light is not scattered as much). The optical window is also referred to as the "visible window" because it overlaps the human visible response spectrum. The
near infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry mom ...
(NIR) window lies just out of the human vision, as well as the medium wavelength infrared (MWIR) window, and the long-wavelength or far-infrared (LWIR or FIR) window, although other animals may perceive them.


History

In the 13th century,
Roger Bacon Roger Bacon (; la, Rogerus or ', also '' Rogerus''; ), also known by the Scholastic accolades, scholastic accolade ''Doctor Mirabilis'', was a medieval England, medieval English philosopher and Franciscans, Franciscan friar who placed consid ...
theorized that
rainbow A rainbow is a meteorology, meteorological phenomenon that is caused by Specular reflection, reflection, refraction and dispersion (optics), dispersion of light in water droplets resulting in a optical spectrum, spectrum of light appearing in ...
s were produced by a similar process to the passage of light through glass or crystal. In the 17th century,
Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician, physicist, astronomer, alchemist, Theology, theologian, and author (described in his time as a "natural philosophy, natural philosopher"), widely ...
discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book ''
Opticks ''Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light'' is a book by English people, English natural philosopher Isaac Newton that was published in English language, English in 1704 (a scholarly Latin transl ...
''. He was the first to use the word ''spectrum'' (
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
for "appearance" or "apparition") in this sense in print in 1671 in describing his
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs wh ...
s in
optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...
. Newton observed that, when a narrow beam of
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible spectrum, visible, and ultraviolet light. On Earth, sunlight is light scattering by particles, scattered and attenuation, filtered t ...
strikes the face of a glass prism at an angle, some is reflected and some of the beam passes into and through the glass, emerging as different-colored bands. Newton hypothesized light to be made up of "corpuscles" (particles) of different colors, with the different colors of light moving at different speeds in transparent matter, red light moving more quickly than violet in glass. The result is that red light is bent (
refracted In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical sci ...
) less sharply than violet as it passes through the prism, creating a spectrum of colors. Newton originally divided the spectrum into six named colors:
red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometre 330px, Different lengths as in respect to the molecula ...
,
orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower *Orange (colour), from the color of an orange, occurs between red and yellow in the visible spectrum * ...
,
yellow Yellow is the color between green and Orange (color), orange on the Visible spectrum, spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 Nanometre, nm. It is a primary color in subtractive color systems, u ...
,
green Green is the color Color (American English) or colour (British English) is the visual perception, visual perceptual Physical property, property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes ...
,
blue Blue is one of the three primary colours in the RYB color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical sp ...
, and violet. He later added
indigo Indigo is a deep color close to the Shades of blue#Blue (RGB) (X11 blue), color wheel blue (a primary color in the RGB color space), as well as to some variants of ultramarine, based on the indigo dye, ancient dye of the same name. The word " ...
as the seventh color since he believed that seven was a perfect number as derived from the
ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek Dark ...
sophists A sophist ( el, σοφιστής, sophistes) was a teacher in ancient Greece in the fifth and fourth centuries BC. Sophists specialized in one or more subject areas, such as Ancient Greek philosophy, philosophy, rhetoric, Music of ancient Greece ...
, of there being a connection between the colors, the musical notes, the known objects in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
, and the days of the week. The human eye is relatively insensitive to indigo's frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some later commentators, including
Isaac Asimov Isaac Asimov ( ; 1920 – April 6, 1992) was an American writer and professor of biochemistry at Boston University. During his lifetime, Asimov was considered one of the "Big Three" science fiction writers, along with Robert A. Heinlein and ...
, have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet. Evidence indicates that what Newton meant by "indigo" and "blue" does not correspond to the modern meanings of those color words. Comparing Newton's observation of prismatic colors to a color image of the visible light spectrum shows that "indigo" corresponds to what is today called blue, whereas his "blue" corresponds to
cyan Cyan () is the color between green and blue on the visible spectrum of light. It is evoked by light with a predominant wavelength between 490 and 520 nanometre, nm, between the wavelengths of green and blue. In the subtractive color system, or ...
. In the 18th century,
Johann Wolfgang von Goethe Johann Wolfgang von Goethe (28 August 1749 – 22 March 1832) was a German people, German poet, playwright, novelist, scientist, politician, statesman, theatre director, and critic. Johann Wolfgang von Goethe bibliography, His works include pla ...
wrote about optical spectra in his ''
Theory of Colours ''Theory of Colours'' (german: Zur Farbenlehre, links=no) is a book by Johann Wolfgang von Goethe about the poet's views on the nature of colours and how these are perceived by humans. It was published in German in 1810 and in English in 1840. ...
''. Goethe used the word ''spectrum'' (''Spektrum'') to designate a ghostly optical
afterimage AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio alb ...
, as did
Schopenhauer Arthur Schopenhauer ( , ; 22 February 1788 – 21 September 1860) was a German philosopher. He is best known for his 1818 work ''The World as Will and Representation'' (expanded in 1844), which characterizes the Phenomenon, phenomenal world ...
in ''
On Vision and Colors ''On Vision and Colors'' (originally translated as ''On Vision and Colours''; german: Ueber das Sehn und die Farben) is a treatise by Arthur Schopenhauer that was published in May 1816 when the author was 28 years old. Schopenhauer had extensive d ...
''. Goethe argued that the continuous spectrum was a compound phenomenon. Where Newton narrowed the beam of light to isolate the phenomenon, Goethe observed that a wider aperture produces not a spectrum but rather reddish-yellow and blue-cyan edges with
white White is the lightest color Color (American English) or colour (British English) is the visual perception, visual perceptual Physical property, property deriving from the spectrum of light interacting with the photoreceptor cells of th ...
between them. The spectrum appears only when these edges are close enough to overlap. In the early 19th century, the concept of the visible spectrum became more definite, as light outside the visible range was discovered and characterized by
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
(
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
) and Johann Wilhelm Ritter (
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
), Thomas Young, Thomas Johann Seebeck, and others. Young was the first to measure the wavelengths of different colors of light, in 1802. The connection between the visible spectrum and
color vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...
was explored by Thomas Young and
Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association ...
in the early 19th century. Their theory of color vision correctly proposed that the eye uses three distinct receptors to perceive color.


Color perception across species

Many species can see light within frequencies outside the human "visible spectrum".
Bee Bees are winged insects closely related to wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which lo ...
s and many other insects can detect ultraviolet light, which helps them find
nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to anim ...
in flowers. Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light rather than how colorful they appear to humans. Birds, too, can see into the ultraviolet (300–400 nm), and some have sex-dependent markings on their plumage that are visible only in the ultraviolet range. Many animals that can see into the ultraviolet range cannot see red light or any other reddish wavelengths. Bees' visible spectrum ends at about 590 nm, just before the orange wavelengths start. Birds can see some red wavelengths, although not as far into the light spectrum as humans.Varela, F. J.; Palacios, A. G.; Goldsmith T. M. (1993
"Color vision of birds"
pp. 77–94 in ''Vision, Brain, and Behavior in Birds'', eds. Zeigler, Harris Philip and Bischof, Hans-Joachim. MIT Press.
The popular belief that the common goldfish is the only animal that can see both infrared and ultraviolet light is incorrect, because goldfish cannot see infrared light. Most mammals are dichromatic, and dogs and horses are often thought to be color blind. They have been shown to be sensitive to colors, though not as many as humans. Some snakes can "see" radiant heat at
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...
s between 5 and 30  μm to a degree of accuracy such that a blind
rattlesnake Rattlesnakes are venomous snakes that form the genus, genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting smal ...
can target vulnerable body parts of the prey at which it strikes, and other snakes with the organ may detect warm bodies from a meter away. It may also be used in
thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
and
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation (wh ...
detection.Greene HW. (1992). "The ecological and behavioral context for pitviper evolution", in Campbell JA, Brodie ED Jr. ''Biology of the Pitvipers''. Texas: Selva. . (See Infrared sensing in snakes)


Spectral colors

Colors that can be produced by visible light of a narrow band of wavelengths ( monochromatic light) are called pure spectral colors. The various color ranges indicated in the illustration are an approximation: The spectrum is continuous, with no clear boundaries between one color and the next.


Color display spectrum

Color displays (e.g.
computer monitor A computer monitor is an output device that displays information in pictorial or textual form. A discrete monitor comprises a electronic visual display, visual display, support electronics, power supply, Housing (engineering), housing, electric ...
s and
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of Transmission (telecommunications), television transmission. Television ...
s) cannot reproduce ''all'' colors discernible by a human eye. Colors outside the color
gamut In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain ''complete subset'' of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circ ...
of the device, such as most spectral colors, can only be approximated.


Spectroscopy

Spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectrum, electromagnetic spectra that result from the interaction between Electromagnetism, electromagnetic radiation and matter as a function of the wavelengt ...
is the study of objects based on the spectrum of color they emit, absorb or reflect. Visible-light spectroscopy is an important tool in
astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
(as is
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectrum, electromagnetic spectra that result from the interaction between Electromagnetism, electromagnetic radiation and matter as a function of the wavelengt ...
at other wavelengths), where scientists use it to analyze the properties of distant objects.
Chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
s and small
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioche ...
s can be detected in astronomical objects by observing
emission line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency range, ...
s and absorption lines. For example,
Helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol (chemistry), symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas gr ...
was first detected by analysis of the spectrum of the
sun The Sun is the star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other st ...
. The shift in frequency of spectral lines is used to measure the
Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer (physics), observer who is moving relative to the wave source. It is named after the Austrian physicist Chri ...
(
redshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...
or
blueshift In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and simultaneous increase in fr ...
) of distant objects to determine their velocities towards or away from the observer.
Astronomical spectroscopy Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the electromagnetic spectrum, spectrum of electromagnetic radiation, including Visible light astronomy, visible light, Ultraviolet astronomy, ult ...
uses high-dispersion
diffraction grating In optics, a diffraction grating is an optical component with a periodic structure that diffraction, diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form ...
s to observe spectra at very high spectral resolutions.


Properties


Heat

Although non-visible infrared light is more commonly thought of as "heat radiation", any frequency of light, including visible light, will heat surfaces that absorb them. A powerful source of purely visible light, such as a visible light laser, can char paper.


Biological effects

High-energy visible light (HEV light) (violet/blue light, with a wavelength of 400-450 nm) has a number of biological effects, especially on the eye. Studies by Harvard Health Publishing and France's ANSES found that exposure to blue light has a negative effect on sleep and can lead to impaired vision.


See also

*
High-energy visible light High-energy visible light (HEV light) is high-frequency, high-photon energy, energy light in the Violet (color), violet/blue band from 400 to 450 nanometre, nm in the visible spectrum, which has a number of biological effects, including those ...
* Electromagnetic absorption by water


References

{{Color topics Color Electromagnetic spectrum Vision