Editing Color temperature (section)

==Categorizing different lighting==
{{Stack|{{Color temperature scale}}}}
[[File:Black body visible spectrum.gif|thumb|300px|The [[black-body]] radiance (B{{sub|λ}}) vs. wavelength (λ) curves for the [[visible spectrum]]. The vertical axes of [[Planck's law]] plots building this animation were proportionally transformed to keep equal areas between functions and horizontal axis for wavelengths 380–780&nbsp;nm.  K indicates the color temperature in [[kelvin]]s, and M indicates the color temperature in micro reciprocal degrees.|right]]

The color temperature of the [[electromagnetic radiation]] emitted from an ideal [[black body]] is defined as its surface temperature in [[kelvin]]s, or alternatively in [[mired|micro reciprocal degree]]s (mired).<ref>{{cite book
| title = Principles of Lighting
| author = Wallace Roberts Stevens
| publisher = Constable
| year = 1951
| url = https://books.google.com/books?id=gH5RAAAAMAAJ&q=micro-reciprocal-degree+date:0-1960 }}
</ref> This permits the definition of a standard by which light sources are compared.

To the extent that a hot surface emits [[thermal radiation]] but is not an ideal black-body radiator, the color temperature of the light is not the actual temperature of the surface. An [[incandescent lamp]]'s light is thermal radiation, and the bulb approximates an ideal black-body radiator, so its color temperature is essentially the temperature of the filament. Thus a relatively low temperature emits a dull red and a high temperature emits the almost white of the traditional incandescent light bulb. Metal workers are able to judge the temperature of hot metals by their color, from dark red to orange-white and then white (see [[red heat]]).

Many other light sources, such as [[fluorescent lamp]]s, or light emitting diodes ([[LED]]s) emit light primarily by processes other than thermal radiation. This means that the emitted radiation does not follow the form of a [[black-body spectrum]]. These sources are assigned what is known as a [[correlated color temperature]] (CCT). CCT is the color temperature of a black-body radiator which to [[color vision|human color perception]] most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from comparison to a black-body radiator.

===The Sun===
The [[Sun]] closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is 5772&nbsp;K.<ref>{{cite web |last=Williams |first=David R. |year=2022 |title=Sun Fact Sheet |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html |publisher=[[NASA]] |access-date=2023-03-24 |url-status=live |archive-url=https://web.archive.org/web/20230316150908/https://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html |archive-date=2023-03-16 }}</ref> The color temperature of [[sunlight]] above the atmosphere is about 5900&nbsp;K.<ref>{{cite web |url=http://www.crisp.nus.edu.sg/~research/tutorial/optical.htm |title=Principles of Remote Sensing |publisher=[[Centre for Remote Imaging, Sensing, and Processing|CRISP]] |access-date=2012-06-18 |url-status=live |archive-url=https://web.archive.org/web/20120702174159/http://www.crisp.nus.edu.sg/~research/tutorial/optical.htm |archive-date=2012-07-02 }}</ref>

The Sun may appear red, orange, yellow, or white from Earth, depending on [[position of the Sun|its position]] in the sky. The changing color of the Sun over the course of the day is mainly a result of the [[scattering]] of sunlight and is not due to changes in black-body radiation. [[Rayleigh scattering]] of sunlight by [[Earth's atmosphere]] causes the blue color of the sky, which tends to scatter blue light more than red light.

Some [[daylight]] in the early [[morning]] and late [[afternoon]] (the [[golden hour (photography)|golden hours]]) has a lower ("warmer") color temperature due to increased [[light scattering by particles|scattering]] of shorter-wavelength sunlight by [[atmospheric particulates]] – an [[optical phenomenon]] called the [[Tyndall effect]].

Daylight has a spectrum similar to that of a black body with a correlated color temperature of 6500&nbsp;K ([[CIE Standard Illuminant D65|D65]] viewing standard) or 5500&nbsp;K (daylight-balanced photographic film standard).

[[File:Color temperature black body 800-12200K.svg|thumb|center|512px|Approximation of the hues of the Planckian locus as a function of the kelvin temperature, rendered with a white point near 6500&nbsp;K, not accounting for [[chromatic adaptation]]]]

For colors based on black-body theory, blue occurs at higher temperatures, whereas red occurs at lower temperatures. This is the opposite of the cultural associations attributed to colors, in which "red" is "hot", and "blue" is "cold".<ref>
{{cite book
 | title = Mastering Digital Flash Photography: The Complete Reference Guide
 | author = Chris George
 | publisher = [[Sterling Publishing|Sterling]]
 | year = 2008
 | isbn = 978-1-60059-209-6
 | page = 11
 | url = https://books.google.com/books?id=j728wJySfyQC&q=blue+cool+red+hot+color-temperature+sun
 }}</ref>