Editing Color (section)

== Physical properties ==

[[File:Visible spectrum 390-710 nm linear perceptual.svg|alt=gray fading to rainbow colors (red to violet), then fade back to gray|center|thumb|600x600px|The visible spectrum perceived from 390 to 710&nbsp;nm [[wavelength]]]]
[[Electromagnetic radiation]] is characterized by its [[wavelength]] (or [[frequency]]) and its [[luminous intensity|intensity]]. When the wavelength is within the [[visible spectrum]] (the range of wavelengths humans can perceive, approximately from 390&nbsp;[[nanometre|nm]] to 700&nbsp;nm), it is known as "visible [[light]]".<ref name="Bettini">{{cite book |last1=Bettini |first1=Alessandro |url=https://books.google.com/books?id=Ip9xDQAAQBAJ&q=%22electromagnetic+waves%22+charges+accelerating&pg=PA95 |title=A Course in Classical Physics, Vol. 4 – Waves and Light |date=2016 |publisher=Springer |isbn=978-3-319-48329-0 |pages=95, 103}}</ref>

Most light sources emit light at many different wavelengths; a source's ''spectrum'' is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color [[wikt:sensation|sensation]] in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation, although such classes would vary widely among different species, and to a lesser extent among individuals within the same species. In each such class, the members are called ''[[metamerism (color)|metamer]]s'' of the color in question. This effect can be visualized by comparing the light sources' [[spectral power distribution]]s and the resulting colors.

=== Spectral colors<span class="anchor" id="Spectral colours"></span> ===
{{main|Spectral color}}
The familiar colors of the [[rainbow]] in the [[visible spectrum|spectrum]]—named using the [[Latin]] word for ''appearance'' or ''apparition'' by [[Isaac Newton]] in 1671—include all those colors that can be produced by visible [[light]] of a single wavelength only, the [[spectral color|''pure spectral'' or ''monochromatic'' color]]s. The spectrum above shows approximate wavelengths (in [[nanometre|nm]]) for spectral colors in the visible range. Spectral colors have 100% [[colorfulness#Excitation purity|purity]], and are fully [[colorfulness|saturate]]d. A complex mixture of spectral colors can be used to describe any color, which is the definition of a light [[power spectrum]].

The spectral colors form a continuous spectrum, and how it is divided into [[color term|distinct colors linguistically]] is a matter of culture and historical contingency.<ref>[[Brent Berlin|Berlin, B.]] and [[Paul Kay|Kay, P.]], ''[[Basic Color Terms: Their Universality and Evolution]]'', Berkeley: [[University of California Press]], 1969.</ref> Despite the ubiquitous [[ROYGBIV]] mnemonic used to remember the spectral colors in English, the inclusion or exclusion of colors is contentious, with disagreement often focused on [[indigo#Classification as a spectral color|indigo]] and cyan.<ref>{{cite book|last=Waldman|first=Gary|title=Introduction to light: the physics of light, vision, and color|year=2002|publisher=Dover Publications|location=Mineola|isbn=978-0486421186|page=193|url=https://books.google.com/books?id=PbsoAXWbnr4C&pg=PA193}}</ref> Even if the subset of color terms is agreed, their wavelength ranges and borders between them may not be.

The ''intensity'' of a spectral color, relative to the context in which it is viewed, may alter its perception considerably. For example, a low-intensity orange-yellow is [[brown]], and a low-intensity yellow-green is [[olive green]]. Additionally, hue shifts towards yellow or blue happen if the intensity of a spectral light is increased; this is called [[Bezold–Brücke shift]]. In [[color models]] capable of representing spectral colors,<ref>{{cite web |title=Perceiving Color |url=http://courses.washington.edu/psy333/lecture_pdfs/chapter7_Color.pdf#page=72 |website=courses.washington.edu}}</ref> such as [[CIELUV]], a spectral color has the maximal saturation. In [[Helmholtz–Kohlrausch effect#Helmholtz color coordinates|Helmholtz coordinates]], this is described as 100% [[Colorfulness#Excitation purity|purity]].

=== Color of objects<span class="anchor" id="Colour of objects"></span> ===

The physical color of an object depends on how it [[absorbance|absorb]]s and [[scattering|scatter]]s light. Most objects scatter light to some degree and do not reflect or transmit light [[specular]]ly like [[glass]]es or [[mirror]]s. A [[transparency (optics)|transparent]] object allows almost all light to [[transmittance|transmit]] or pass through, thus transparent objects are perceived as colorless. Conversely, an [[opacity (optics)|opaque]] object does not allow light to transmit through and instead absorbs or [[reflection (physics)|reflects]] the light it receives. Like transparent objects, [[translucent]] objects allow light to transmit through, but translucent objects are seen colored because they scatter or absorb certain wavelengths of light via internal scattering. The absorbed light is often dissipated as [[heat]].<ref name=":0">{{Cite book |last=Berns |first=Roy S. |url= |title=Billmeyer and Saltzman's Principles of Color Technology |publisher=[[Wiley (publisher)|Wiley]] |others=Fred W. Billmeyer, Max Saltzman |year=2019 |isbn=978-1119366683 |edition=4th |location=Hoboken, NJ |oclc=1080250734|pages=5–9, 12}}</ref>