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[[Image:Srgbspectrum.png|centre|sRGB rendering of the spectrum of visible light]]
 
The '''visible spectrum''' (or sometimes called the '''optical spectrum''') is the portion of the [[electromagnetic spectrum]] that is [[visual perception|visible]] to (can be detected by) the human [[eye]]. [[Electromagnetic radiation]] in this range of [[wavelength]]s is called '''visible light''' or simply [[light]]. A typical human eye will respond to wavelengths in [[air]] from about [[1 E-7 m|380 to 750&nbsp;nm]].<ref>{{cite book | title = Biology: Concepts and Applications | author = Cecie Starr | publisher = Thomson Brooks/Cole | year = 2005 | isbn = 053446226X | url = http://books.google.com/books?id=RtSpGV_Pl_0C&pg=PA94&dq=380+750+visible+wavelengths&as_brr=3&ei=g7x0R5erIISOsgOtsLGeBw&ie=ISO-8859-1&sig=wJ7g0EcU-QUF29vfvl36YNg-FtU }}</ref> The corresponding wavelengths in [[water]] and other media are reduced by a factor equal to the [[refractive index]]. In terms of frequency, this corresponds to a band in the vicinity of 400-790 [[terahertz]]. A [[light]]-adapted eye generally has its maximum sensitivity at around 555&nbsp;[[nanometre|nm]] (540 THz), in the [[green]] region of the optical spectrum (see: [[luminosity function]]). The spectrum does not, however, contain all the [[color]]s that the human eyes and brain can distinguish. [[Brown]], [[pink]], and [[magenta]] are absent, for example, because they need a mix of multiple wavelengths, preferably shades of red.
 
 
[[Image:PrismAndLight.jpg|thumb|right|300px|White [[light]] dispersed by a [[triangular prism (optics)|prism]] into the colors of the optical spectrum.]]
 
  
Wavelengths visible to the eye also pass through the "[[optical window]]", the region of the electromagnetic spectrum which passes largely unattenuated through the [[Earth's atmosphere]] (although blue light is [[scattering|scattered]] more than red light, which is the reason the sky is blue). The response of the human eye is defined by subjective testing (see [[International Commission on Illumination|CIE]]), but the atmospheric windows are defined by physical measurement.  The "visible window" is so called because it overlaps the human visible response spectrum; the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region.
 
  
The eyes of many [[species]] perceive wavelengths different from the spectrum visible to the human eye. For example, many [[insect]]s, such as [[bee]]s, can see light in the [[ultraviolet]], which is useful for finding [[nectar (plant)|nectar]] in [[flower]]s. For this reason, plant species whose life cycles are linked to insect pollination may owe their reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to our eyes.
+
==Overview==
 +
The '''visible spectrum''' (or sometimes called the '''optical spectrum''') is the portion of the [[electromagnetic spectrum]] that is [[visual perception|visible]] to (can be detected by) the human [[eye]]. [[Electromagnetic radiation]] in this range of [[wavelength]]s is called '''visible light''' or simply [[light]]. A typical human eye will respond to wavelengths in [[air]] from about [[1 E-7 m|380 to 750&nbsp;nm]].<ref>{{cite book | title = Biology: Concepts and Applications | author = Cecie Starr | publisher = Thomson Brooks/Cole | year = 2005 | isbn = 053446226X | url = http://books.google.com/books?id=RtSpGV_Pl_0C&pg=PA94&dq=380+750+visible+wavelengths&as_brr=3&ei=g7x0R5erIISOsgOtsLGeBw&ie=ISO-8859-1&sig=wJ7g0EcU-QUF29vfvl36YNg-FtU }}</ref> The corresponding wavelengths in [[water]] and other media are reduced by a factor equal to the [[refractive index]]. In terms of frequency, this corresponds to a band in the vicinity of 400-790 terahertz. A [[light]]-adapted eye generally has its maximum sensitivity at around 555&nbsp;[[nanometre|nm]] (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the [[color]]s that the human eyes and brain can distinguish. Brown, pink, and magenta are absent, for example, because they need a mix of multiple wavelengths, preferably shades of red.
 +
 
 +
Wavelengths visible to the eye also pass through the "optical window", the region of the electromagnetic spectrum which passes largely unattenuated through the [[Earth's atmosphere]] (although blue light is [[scattering|scattered]] more than red light, which is the reason the sky is blue). The response of the human eye is defined by subjective testing (see CIE), but the atmospheric windows are defined by physical measurement.  The "visible window" is so called because it overlaps the human visible response spectrum; the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region.
 +
 
 +
The eyes of many [[species]] perceive wavelengths different from the spectrum visible to the human eye. For example, many [[insect]]s, such as [[bee]]s, can see light in the [[ultraviolet]], which is useful for finding nectar in [[flower]]s. For this reason, plant species whose life cycles are linked to insect pollination may owe their reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to our eyes.
  
 
== History ==
 
== History ==
Two of the earliest explanations of the optical spectrum came from [[Isaac Newton]], when he wrote his ''[[Opticks]]'', and from [[Johann Wolfgang Goethe|Goethe]], in his ''[[Theory of Colours]]'', although earlier observations had been made by [[Roger Bacon]] who first recognized the visible spectrum in a glass of water, four centuries before Newton discovered that prisms could disassemble and reassemble white light.{{Fact|date=October 2007}}
+
Two of the earliest explanations of the optical spectrum came from [[Isaac Newton]], when he wrote his ''Opticks'', and from Goethe, in his ''Theory of Colours'', although earlier observations had been made by Roger Bacon who first recognized the visible spectrum in a glass of water, four centuries before Newton discovered that prisms could disassemble and reassemble white light.
 
 
[[Image:Newton's colour circle.png|thumb|250px|right|Newton's color circle, showing the colors correlated with musical notes and symbols for the planets.  The spectrum aligns with the colors from violet, around the circle, to red, but Newton's circle failed to indicate the discontinuity in closing the circle from red back to violet; this is where the [[purple]] colors fall.]]
 
  
Newton first used the word ''spectrum'' ([[Latin]] for "appearance" or "apparition") in print in 1671 in describing his [[experiment]]s in [[optic]]s.  Newton observed that, when a narrow beam of [[sunlight]] strikes the face of a [[glass]] [[triangular prism (optics)|prism]] at an [[angle]], some is [[Reflection (physics)|reflected]] and some of the beam passes into and through the glass, emerging as different colored bands.  Newton hypothesized that light was made up of "[[corpuscle]]s" (particles) of different colors, and that the different colors of light moved at different speeds in transparent matter, with red light moving more quickly in glass than violet light. The result is that red light was bent ([[refraction|refracted]]) less sharply than violet light as it passed through the prism, creating a spectrum of colors.  
+
Newton first used the word ''spectrum'' ([[Latin]] for "appearance" or "apparition") in print in 1671 in describing his [[experiment]]s in [[optic]]s.  Newton observed that, when a narrow beam of [[sunlight]] strikes the face of a [[glass]] [[triangular prism (optics)|prism]] at an [[angle]], some is [[Reflection (physics)|reflected]] and some of the beam passes into and through the glass, emerging as different colored bands.  Newton hypothesized that light was made up of "corpuscles" (particles) of different colors, and that the different colors of light moved at different speeds in transparent matter, with red light moving more quickly in glass than violet light. The result is that red light was bent ([[refraction|refracted]]) less sharply than violet light as it passed through the prism, creating a spectrum of colors.  
  
Newton divided the spectrum into seven named colors: [[red]], [[Orange (colour)|orange]], [[yellow]], [[green]], [[blue]], [[indigo]], and [[Violet (color)|violet]] (this order being popularly memorised by schoolchildren using the mnemonic [[ROY G. BIV]]). He chose seven colors out of a belief, derived from the ancient Greek [[sophists]], that there was a connection between the colors, the musical notes, the known objects in the [[solar system]], and the days of the week.<ref>{{cite web|url=http://home.vicnet.net.au/~colmusic/opticks3.htm |title=Music For Measure: On the 300th Anniversary of Newton's ''Opticks'' |accessdate=2006-08-11 |last=Hutchison |first=Niels |year=2004 |work=Colour Music }}</ref><ref>{{cite book |last=Newton |first=Isaac |authorlink=Isaac Newton |title=[[Opticks]] |year=1704 }}</ref> The human eye is relatively insensitive to indigo's frequencies, and some otherwise well-sighted people cannot distinguish indigo from blue and violet. For this reason some commentators including [[Isaac Asimov]] have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.
+
Newton divided the spectrum into seven named colors: red, orange, yellow, green, blue, indigo, and violet (this order being popularly memorised by schoolchildren using the mnemonic ROY G. BIV). He chose seven colors out of a belief, derived from the ancient Greek sophists, that there was a connection between the colors, the musical notes, the known objects in the solar system, and the days of the week.<ref>{{cite web|url=http://home.vicnet.net.au/~colmusic/opticks3.htm |title=Music For Measure: On the 300th Anniversary of Newton's ''Opticks'' |accessdate=2006-08-11 |last=Hutchison |first=Niels |year=2004 |work=Colour Music }}</ref><ref>{{cite book |last=Newton |first=Isaac |authorlink=Isaac Newton |title=Opticks |year=1704 }}</ref> The human eye is relatively insensitive to indigo's frequencies, and some otherwise well-sighted people cannot distinguish indigo from blue and violet. For this reason some commentators including Isaac Asimov have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.
  
[[Johann Wolfgang von Goethe]] contended that the continuous spectrum was a compound phenomenon. Whereas Newton narrowed the beam of light in order to isolate the phenomenon, Goethe observed that with a wider aperture, there was no spectrum - rather there were reddish-yellow edges and blue-cyan edges with [[white]] between them, and the spectrum only arose when these edges came close enough to overlap.  
+
Johann Wolfgang von Goethe contended that the continuous spectrum was a compound phenomenon. Whereas Newton narrowed the beam of light in order to isolate the phenomenon, Goethe observed that with a wider aperture, there was no spectrum - rather there were reddish-yellow edges and blue-cyan edges with white between them, and the spectrum only arose when these edges came close enough to overlap.  
  
All light travels at the same speed in a [[vacuum]].  The [[speed of light]] within a material is lower than the speed of light in a vacuum, and the ratio of speeds is known as the [[refractive index]] of the material.  Because the [[refractive index]] (and thus the speed) of a wave in a material depends on its [[frequency]] (in accordance with a [[dispersion relation]]), light consisting of multiple frequencies—for instance white light—will be [[dispersion (optics)|dispersed]] at the interface between the material and air or vacuum.  Both water and glass can be used to demonstrate dispersion; a glass [[prism]] yields an optical spectrum from white light, and [[rainbow]]s are an ideal example of natural refraction of the visible spectrum.
+
All light travels at the same speed in a [[vacuum]].  The [[speed of light]] within a material is lower than the speed of light in a vacuum, and the ratio of speeds is known as the [[refractive index]] of the material.  Because the [[refractive index]] (and thus the speed) of a wave in a material depends on its [[frequency]] (in accordance with a dispersion relation), light consisting of multiple frequencies—for instance white light—will be [[dispersion (optics)|dispersed]] at the interface between the material and air or vacuum.  Both water and glass can be used to demonstrate dispersion; a glass prism yields an optical spectrum from white light, and [[rainbow]]s are an ideal example of natural refraction of the visible spectrum.
  
 
==Spectral colors==
 
==Spectral colors==
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==Spectroscopy==
 
==Spectroscopy==
[[Image:Atmospheric electromagnetic transmittance or opacity.jpg|thumb|300px|Rough plot of [[Earth]]'s [[Earth's atmosphere|atmospheric]] transmittance (or [[Opacity (optics)|opacity]]) to various [[wavelength]]s of [[electromagnetic radiation]], including [[visible light]].]]
+
The scientific study of objects based on the spectrum of the light they emit is called [[spectroscopy]].  One particularly important application of spectroscopy is in [[astronomy]], where spectroscopy is essential for analysing the properties of distant objects.  Typically, astronomical spectroscopy utilises high-dispersion [[diffraction grating]]s to observe spectra at very high spectral resolutions.  [[Helium]] was first detected through an analysis of the spectrum of the Sun; [[chemical element]]s can be detected in astronomical objects by [[emission line]]s and [[absorption line]]s; the shifting of spectral lines can be used to measure the redshift or blueshift of distant or fast-moving objects.  The first exoplanets to be discovered were found by analysing the doppler shift of stars at such a high resolution that variations in their radial velocity as small as a few metres per second could be detected: the presence of planets was revealed by their gravitational influence on the stars analysed, as revealed by their motion paths.
 
 
The scientific study of objects based on the spectrum of the light they emit is called [[spectroscopy]].  One particularly important application of spectroscopy is in [[astronomy]], where spectroscopy is essential for analysing the properties of distant objects.  Typically, [[astronomical spectroscopy]] utilises high-dispersion [[diffraction grating]]s to observe spectra at very high spectral resolutions.  [[Helium]] was first detected through an analysis of the spectrum of the [[Sun]]; [[chemical element]]s can be detected in astronomical objects by [[emission line]]s and [[absorption line]]s; the shifting of spectral lines can be used to measure the [[redshift]] or [[blueshift]] of distant or fast-moving objects.  The first [[exoplanet]]s to be discovered [[Methods of detecting extrasolar planets#radial velocity|were found by]] analysing the [[doppler shift]] of stars at such a high resolution that variations in their [[radial velocity]] as small as a few [[meters per second|metres per second]] could be detected: the presence of planets was revealed by their [[gravity|gravitational]] influence on the stars analysed, as revealed by their motion paths.
 
  
 
==Color display spectrum==
 
==Color display spectrum==
[[Image:Computer color spectrum.svg|thumb|400px|right|Color display ''spectrum''. The narrow red, green and blue bars show the relative mixture of the three primary colors used to produce the color directly above.]]
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Color displays (e.g., computer monitors or televisions) mix red, green, and blue color to approximate the color spectrum. In the illustration, the narrow red, green and blue bars show the relative mixture of these three colors used to produce the color directly above.
Color displays (e.g., [[computer monitors]] or [[televisions]]) mix [[red]], [[green]], and [[blue]] color to approximate the color spectrum. In the illustration, the narrow red, green and blue bars show the relative mixture of these three colors used to produce the color directly above.
 
  
 
==See also==
 
==See also==
{{wikisourcepar|Littell's Living Age/Volume 145/Issue 1869/Definition of the Color Indigo|a debate whether indigo is the color meant on the spectrum}}
 
 
* [[Color vision]]
 
* [[Color vision]]
 
* [[High-energy visible light]]
 
* [[High-energy visible light]]
* [[Theory of Colours]]
 
  
 
==References==
 
==References==
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{{EMSpectrum}}
 
{{EMSpectrum}}
 
{{Color vision}}
 
{{Color vision}}
 
[[Category:Color]]
 
 
[[Category:Electromagnetic spectrum]]
 
[[Category:Electromagnetic spectrum]]
[[Category:Optical spectrum|*]]
 
 
[[Category:Vision]]
 
[[Category:Vision]]
  
[[bg:Видим спектър]]
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{{WikiDoc Sources}}
[[ca:Espectre visible]]
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[[de:Lichtspektrum]]
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{{WH}}
[[es:Espectro visible]]
 
[[eo:Videbla spektro]]
 
[[hi:प्रत्यक्ष वर्णक्रम]]
 
[[fr:Lumière visible]]
 
[[ko:가시광선]]
 
[[id:Spektrum optik]]
 
[[it:Spettro visibile]]
 
[[ja:可視光線]]
 
[[no:Visuelt spektrum]]
 
[[pl:Światło widzialne]]
 
[[pt:Espectro visível]]
 
[[ru:Видимое излучение]]
 
[[ro:Spectru vizibil]]
 
[[simple:Visible light]]
 
[[sk:Optické spektrum]]
 
[[fi:Värispektri]]
 
[[sv:Spektrum]]
 
[[uk:Видиме світло]]
 
[[zh-yue:可見光]]
 
[[zh:可见光]]
 

Latest revision as of 17:23, 20 August 2012

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Overview

The visible spectrum (or sometimes called the optical spectrum) is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths in air from about 380 to 750 nm.[1] The corresponding wavelengths in water and other media are reduced by a factor equal to the refractive index. In terms of frequency, this corresponds to a band in the vicinity of 400-790 terahertz. A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Brown, pink, and magenta are absent, for example, because they need a mix of multiple wavelengths, preferably shades of red.

Wavelengths visible to the eye also pass through the "optical window", the region of the electromagnetic spectrum which passes largely unattenuated through the Earth's atmosphere (although blue light is scattered more than red light, which is the reason the sky is blue). The response of the human eye is defined by subjective testing (see CIE), but the atmospheric windows are defined by physical measurement. The "visible window" is so called because it overlaps the human visible response spectrum; the near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region.

The eyes of many species perceive wavelengths different from the spectrum visible to the human eye. For example, many insects, such as bees, can see light in the ultraviolet, which is useful for finding nectar in flowers. For this reason, plant species whose life cycles are linked to insect pollination may owe their reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to our eyes.

History

Two of the earliest explanations of the optical spectrum came from Isaac Newton, when he wrote his Opticks, and from Goethe, in his Theory of Colours, although earlier observations had been made by Roger Bacon who first recognized the visible spectrum in a glass of water, four centuries before Newton discovered that prisms could disassemble and reassemble white light.

Newton first used the word spectrum (Latin for "appearance" or "apparition") in print in 1671 in describing his experiments in optics. Newton observed that, when a narrow beam of sunlight 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 that light was made up of "corpuscles" (particles) of different colors, and that the different colors of light moved at different speeds in transparent matter, with red light moving more quickly in glass than violet light. The result is that red light was bent (refracted) less sharply than violet light as it passed through the prism, creating a spectrum of colors.

Newton divided the spectrum into seven named colors: red, orange, yellow, green, blue, indigo, and violet (this order being popularly memorised by schoolchildren using the mnemonic ROY G. BIV). He chose seven colors out of a belief, derived from the ancient Greek sophists, that there was a connection between the colors, the musical notes, the known objects in the solar system, and the days of the week.[2][3] The human eye is relatively insensitive to indigo's frequencies, and some otherwise well-sighted people cannot distinguish indigo from blue and violet. For this reason some commentators including Isaac Asimov have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or violet.

Johann Wolfgang von Goethe contended that the continuous spectrum was a compound phenomenon. Whereas Newton narrowed the beam of light in order to isolate the phenomenon, Goethe observed that with a wider aperture, there was no spectrum - rather there were reddish-yellow edges and blue-cyan edges with white between them, and the spectrum only arose when these edges came close enough to overlap.

All light travels at the same speed in a vacuum. The speed of light within a material is lower than the speed of light in a vacuum, and the ratio of speeds is known as the refractive index of the material. Because the refractive index (and thus the speed) of a wave in a material depends on its frequency (in accordance with a dispersion relation), light consisting of multiple frequencies—for instance white light—will be dispersed at the interface between the material and air or vacuum. Both water and glass can be used to demonstrate dispersion; a glass prism yields an optical spectrum from white light, and rainbows are an ideal example of natural refraction of the visible spectrum.

Spectral colors

Color Wavelength
violet 380–450 nm
blue 450–495 nm
green 495–570 nm
yellow 570–590 nm
orange 590–620 nm
red 620–750 nm

The familiar colors of the rainbow in the spectrum include all those colors that can be produced by visible light of a single wavelength only, the pure spectral or monochromatic colors.

Although the spectrum is continuous and therefore there are no clear boundaries between one color and the next, the ranges may be used as an approximation.[4]

Spectroscopy

The scientific study of objects based on the spectrum of the light they emit is called spectroscopy. One particularly important application of spectroscopy is in astronomy, where spectroscopy is essential for analysing the properties of distant objects. Typically, astronomical spectroscopy utilises high-dispersion diffraction gratings to observe spectra at very high spectral resolutions. Helium was first detected through an analysis of the spectrum of the Sun; chemical elements can be detected in astronomical objects by emission lines and absorption lines; the shifting of spectral lines can be used to measure the redshift or blueshift of distant or fast-moving objects. The first exoplanets to be discovered were found by analysing the doppler shift of stars at such a high resolution that variations in their radial velocity as small as a few metres per second could be detected: the presence of planets was revealed by their gravitational influence on the stars analysed, as revealed by their motion paths.

Color display spectrum

Color displays (e.g., computer monitors or televisions) mix red, green, and blue color to approximate the color spectrum. In the illustration, the narrow red, green and blue bars show the relative mixture of these three colors used to produce the color directly above.

See also

References

  1. Cecie Starr (2005). Biology: Concepts and Applications. Thomson Brooks/Cole. ISBN 053446226X.
  2. Hutchison, Niels (2004). "Music For Measure: On the 300th Anniversary of Newton's Opticks". Colour Music. Retrieved 2006-08-11.
  3. Newton, Isaac (1704). Opticks.
  4. Thomas J. Bruno, Paris D. N. Svoronos. CRC Handbook of Fundamental Spectroscopic Correlation Charts. CRC Press, 2005.




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