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Encyclopedia > Color temperature
The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature
The CIE 1931 x,y chromaticity space, also showing the chromaticities of black-body light sources of various temperatures, and lines of constant correlated color temperature

Color temperature is a characteristic of visible light that has important applications in photography, videography, publishing and other fields. The color temperature of a light source is determined by comparing its chromaticity with a theoretical, heated black-body radiator. The temperature (in kelvin) at which the heated black-body radiator matches the color of the light source is that source's color temperature; for a black body source, it is directly related to Planck's law. Download high resolution version (1300x1462, 524 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1300x1462, 524 KB) Wikipedia does not have an article with this exact name. ... In the study of the perception of color, one of the first mathematically defined color spaces was the CIE XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... Chromaticity is the quality of a color as determined by its purity and dominant wavelength. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... For other uses, see Kelvin (disambiguation). ... Black body spectrum For a general introduction, see black body. ...

Contents

Categorizing different lighting:

Because it is the standard against which other light sources are compared, the color temperature of the thermal radiation from an ideal black-body radiator is defined as equal to its surface temperature in kelvin, using the temperature scale named after the 19th-century British physicist William Thomson, 1st Baron Kelvin. For bodies other than ideal black bodies, the color temperature of the thermal radiation emitted from it may differ from its actual surface temperature. In an incandescent light bulb the light is of thermal origin and is very close to that of an ideal black-body radiator. In physics, a black body is an object that absorbs all electromagnetic radiation that falls onto it. ... For other persons named William Thomson, see William Thomson (disambiguation). ... “Radiant heat” redirects here. ... Light bulb redirects here. ...


However, many other light sources, such as fluorescent lamps, do not primarily emit light because of the temperature of the source and the emitted radiation do not follow the form of a black-body spectrum, and are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black body radiator which in the perception of the human eye 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 the comparison to a black-body radiator. Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... Black body spectrum For a general introduction, see black body. ... Color temperature is a characteristic of visible light that has important applications in photography, videography, publishing and other fields. ... Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. ...


As the sun crosses the sky, it may appear to be red, orange, yellow or white depending on its position. The changing color of the sun over the course of the day is mainly a result of refraction and, to a lesser extent, scattering of light, and is unrelated to black body radiation. Sol redirects here. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...


Even when the sun is low over the horizon, we can estimate its apparent color temperature and correct it to compute its effective temperature. So, even if the sun looks red, and showing an apparent color temperature of 2500 K, a calculation can demonstrate that its effective temperature is in reality close to 5770 K. The effective temperature of a star is the temperature of a black body with the same luminosity (L) as the star and is defined according to the Stefan-Boltzman law L = sigma T_{eff}^{4}. The effective temperature of our Sun is around 5,800 kelvins (K) and correspond to...


The blue color of the sky is not due to black-body radiation, but rather to Rayleigh scattering of the sunlight from the atmosphere, which tends to scatter blue light more than red. This phenomenon has nothing to do with the properties of a black body. Rayleigh scattering causing the blue hue of the sky and the reddening at sunset Rayleigh scattering (named after Lord Rayleigh) is the scattering of light, or other electromagnetic radiation, by particles much smaller than the wavelength of the light. ...

The colors shown are approximate and symbolic, not colorimetrically accurate. A colorimetrically-accurate diagram is available. Image File history File links No higher resolution available. ...


Some common examples.

  • 1700 K: Match flame
  • 1850 K: Candle
  • 2800 K: Tungsten lamp (incandescent lightbulb)
  • 3350 K: Studio "CP" light
  • 3400 K: Studio lamps, photofloods, etc...
  • 4100 K: Moonlight
  • 5000 K: Typical warm daylight
  • 5500–6000 K: Typical cool daylight, electronic flash (can vary between manufacturers)
  • 6420 K: Xenon arc lamp
  • 6500 K: Daylight°
  • 9300 K: TV screen (analog)

The colors of 5000 K and 6500 K black bodies are close to the colors of the standard illumininants called respectively D50 and D65, which are used in professions working with color reproduction (photographers, publishers, etc.). One of the standard illuminants defined by the International Commission on Illumination (CIE) inside a series of illuminants called D series that try to portrait standard illuminanting conditions at open air in different parts of the world. ...


For colors based on the black body, blue is the "hotter" color, while red is actually the "cooler" color. This is the opposite of the cultural associations that colors have taken on, with "red" as "hot", and "blue" as "cold". The traditional associations come from a variety of sources, such as water and ice appearing blue, while heated metal and fire are of a reddish hue. However, the redness of these heat sources comes precisely from the fact that red is the coolest of the visible colors: the first color emitted as heat increases. To see this, observe that while incandescent bulbs glow a reddish to yellowish color throughout their lifetimes, when one blows out, the flash of light is noticeably bluish - the filament is hotter when it burns out, as evidenced by the scorch mark often left on the glass. For other uses, see Fire (disambiguation). ...


"Color temperature" is sometimes used loosely to mean "white balance" or "white point". Notice that color temperature has only one degree of freedom, whereas white balance has two (R-Y and B-Y). A white point is one of a number of reference illuminants used in colorimetry which serve to define the color white. Depending on the application, different definitions of white are needed to give acceptable results. ... Degrees of freedom is a general term used in explaining dependence on parameters, and implying the possibility of counting the number of those parameters. ...


In photography, an alternative numerical measure used is the mired (micro reciprocal degrees). Color temperatures and mireds are convertible to each other via a simple formula (see the mired page for details of the computations, and the reasons for the use of the alternative unit). Photography [fәtɑgrәfi:],[foʊtɑgrәfi:] is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor. ... Derived from the term micro reciprocal degree, the mired (M) is a unit of measurement equal to 1,000,000 (one million) divided by the given color temperature, as per the formula: where M is the mired value desired, and T is the color temperature. ... Derived from the term micro reciprocal degree, the mired (M) is a unit of measurement equal to 1,000,000 (one million) divided by the given color temperature, as per the formula: where M is the mired value desired, and T is the color temperature. ...


Color temperature applications

Film photography

Film sometimes exaggerates the color of the light. An object that appears to the naked eye to be under white light may turn out looking very blue or orange in a photograph. The color balance may need to be corrected while shooting to achieve a neutral color print. In photography and image processing, color balance (sometimes gray balance, neutral balance, or white balance) refers to the adjustment of the relative amounts of red, green, and blue primary colors in an image such that neutral colors are reproduced correctly. ...


Film is made for specific light sources (most commonly daylight film and tungsten film), and used properly, will create a neutral color print. Matching the color sensitivity of the film to the color temperature of the light source is one way to balance color. If tungsten film is used indoors with incandescent lamps, the yellowish-orange light of the tungsten [incandescent] bulbs will appear as white (3200 K) in the photograph. Tungsten film is designed to give accurate colors under tungsten light. ... Incandescence is the release of electromagnetic radiation from a hot body due to its high temperature. ... For other uses, see Tungsten (disambiguation). ...


Filters on a camera lens, or color gels over the light source(s) may also be used to correct color balance. When shooting with a bluish light (high temperature) source such as on an overcast day, in the shade, in window light or if using tungsten film with white or blue light, a yellowish-orange filter will correct this. For shooting with daylight film (calibrated to 5600 K) under warmer (low temperature) light sources such as sunsets, candle light or tungsten lighting, a bluish (e.g. #80A) filter may be used. In photography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. ... A color gel or color filter (US color gel or color filter), or a lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to colour light and for color correction. ...


Fluorescent light varies in color and may be harder to correct for. Because it is often greenish, a magenta filter may correct it, though this could take some trial and error.


If there is more than one light source with varied color temperatures, gels (placed over each light source) in conjunction with daylight film is the best way to balance the color.


Desktop publishing

In the desktop publishing industry, it is important to know your monitor’s color temperature. Color matching software, such as ColorSync will measure a monitor's color temperature and then adjust its settings accordingly. This enables on-screen color to more closely match printed color. Common monitor color temperatures are as follows: ColorSync is Apples color management API for the Mac OS and Mac OS X. // Apple developed the original 1. ...


5000 K (D50), 5500 K (D55), 6500 K (D65), 7500 K (D75) and 9300 K. One of the standard illuminants defined by the International Commission on Illumination (CIE) inside a series of illuminants called D series that try to portrait standard illuminanting conditions at open air in different parts of the world. ...


Designations such as D50 are used to classify color temperatures of light tables and viewing booths. When viewing a color slide at a light table, it is important that the light be balanced properly so that the colors are not shifted towards the red or blue. A light table is a viewing device that is used to review photographic film or artwork placed on top of it. ... A single slide, showing a color transparency in a plastic frame In photography, a reversal film is a still, positive image created on a transparent base using photochemical means. ...


Digital cameras, web graphics, and DVDs etc. are normally designed for a 6500 K color temperature & indeed the sRGB standard stipulates (among other things) a 6500 K display whitepoint. Look up digital camera in Wiktionary, the free dictionary. ... DVD (also known as Digital Versatile Disc or Digital Video Disc) is a popular optical disc storage media format. ... CIE 1931 xy chromaticity diagram showing the gamut of the sRGB color space and location of the primaries. ...


TV, video, and digital still cameras

The NTSC and PAL TV norms call for a compliant TV screen to display an electrically "black-and-white" signal (minimal color saturation) at a color temperature of 6500K. On many actual sets however, especially older and/or cheaper ones, there is a very noticeable deviation from this requirement. NTSC is the analog television system in use in Canada, Japan, Mexico, the Philippines, South Korea, Taiwan, the United States, and some other countries, mostly in the Americas (see map). ... For other uses, see PAL (disambiguation). ...


Most video and digital still cameras can adjust for color temperature by zooming into a white or neutral colored object and setting the manual "white balance" (telling the camera that "this object is white"); the camera then shows true white as white and adjusts all the other colors accordingly. White-balancing is necessary especially when indoors under fluorescent lighting and when moving the camera from one lighting situation to another. The setting called "Auto white balance" is not recommended for optimum quality video or stills.


Artistic application via control of color temperature

The house above appears a light cream during the midday, but seems a bluish white here in the dim light before full sunrise. Note the different color temperature of the sunrise in the background.

Experimentation with color temperature is obvious in many Stanley Kubrick films; for instance in Eyes Wide Shut the light coming in from a window was almost always conspicuously blue, whereas the light from lamps on end tables was fairly orange. Indoor lights typically give off a yellow hue; fluorescent and natural lighting tends to be more blue. The house in this picture appears a light cream color during the day, but looks a bluish white here, just after dawn. ... The house in this picture appears a light cream color during the day, but looks a bluish white here, just after dawn. ... Kubrick redirects here. ... Eyes Wide Shut is a 1999 film directed and co-written by Stanley Kubrick, based on the novella Traumnovelle (in English Dream Story) by Arthur Schnitzler. ...


Video camera operators can also white-balance objects which aren't white, downplaying the color of the object used for white-balancing. For instance, they can bring more warmth into a picture by white-balancing off something light blue, such as faded blue denim; in this way white-balancing can serve in place of a filter or lighting gel when those aren't available. A Camera Operator uses a camera to capture moving images in events and scenes. ...


Cinematographers do not "white balance" in the same way as video camera operators: they can use techniques such as filters, choice of film stock, pre-flashing, and after shooting, color grading (both by exposure at the labs, and also digitally, where digital film processes are used). Cinematographers also work closely with set designers and lighting crews to achieve their desired effects. Cameraman redirects here. ... In cinematography and photography, pre-flashing is the exposure of the film or other photosensor to uniform light prior to exposing it to the scene to be imaged. ... Color grading is the process of altering and enhancing the color of a motion picture or television image, either electronically, photo-chemically or digitally. ... Digital film refers to cinema production and performance systems which work by using a digital representation of the brightness and colour of each pixel of the image. ...


For artists, most pigments and papers have a cool or warm cast, as the human eye can detect even a minute amount of saturation. Gray mixed with yellow, orange or red is a "warm gray". Green, blue, or purple, create "cool grays".

WARM GRAY COOL GRAY
Mixed with 6% yellow. Mixed with 6% blue.

Image File history File links No higher resolution available. ...

Correlated color temperature

CIE (1931) xy chromaticity diagram including the Planckian locus, with temperatures indicated. Wavelengths of monochromatic light are shown in blue. The lines crossing the Planckian locus are lines of constant correlated color temperature.
CIE (1931) xy chromaticity diagram including the Planckian locus, with temperatures indicated. Wavelengths of monochromatic light are shown in blue. The lines crossing the Planckian locus are lines of constant correlated color temperature.

Incandescent lamps are well described by their temperature on the Kelvin scale, because as nearly black-body radiators, their chromaticity coordinates land directly on the Planckian locus of the CIE 1931 (x, y) chromaticity diagram. Fluorescent lighting is not incandescent and presents a new challenge. Fluorescent lamps are made using myriad combinations of phosphors and gases. The illumination that they produce is almost never described by a point in color space that lies on the Planckian locus. Download high resolution version (1300x1462, 524 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1300x1462, 524 KB) Wikipedia does not have an article with this exact name. ... In Color theory, the Planckian locus is generally the path that the color of a black body would take in a particular color space as the blackbody temperature changes. ... In the study of the perception of color, one of the first mathematically defined color spaces was the CIE XYZ color space (also known as CIE 1931 color space), created by the International Commission on Illumination (CIE) in 1931. ... Fluorescent lamps in Shinbashi, Tokyo, Japan Assorted types of fluorescent lamps. ... Green screen A phosphor is a substance that exhibits the phenomenon of phosphorescence (sustained glowing after exposure to light or energised particles such as electrons). ...


The question then becomes how to describe the quality of light from a fluorescent lamp. The method used is called the "correlated color temperature", which is a method for assigning a color temperature to a color near, but not on, the Planckian locus. The above plot shows lines crossing the Planckian locus for which the correlated color temperature is the same. Nevertheless, the colors are not the same, and the method gives only an approximate specification of a particular color. Due to this shortcoming, the rated CCT of any fluorescent tube does not completely specify its color.


To be more precise: A number of color spaces have been developed in which the distance between them on a chromaticity diagram may estimate the difference between two colors. These include the CIE 1960 uv chromaticity diagram and the CIE 1976 u'v' chromaticity diagram. On a chromaticity diagram for which distances specify color distances, the best estimate of the color temperature of any point will be the color temperature of the point on the Planckian locus closest to that point. Although it is outdated, the CIE specifies distances in the 1960 uv chromaticity space to define correlated color temperature. Lab is the abbreviated name of two different color spaces. ...


Photographers often use color temperature meters. Color temperature meters are designed to read only two regions along the visible spectrum (red & blue), more expensive ones read three regions (red, green & blue). They are almost useless under fluorescent light. There are general guidelines and some specific filters recommended to obtain optimum quality under such frustrating circumstances.


Color rendering index

Main article: Color rendering index

The CIE developed a newer model for describing and rating light sources, called the color rendering index (CRI), which is a mathematical formula describing how well a light source's illumination of eight sample patches compares to the illumination provided by a reference source. The index provides a number up to 100 for ideal light. This index is useful in determining the suitability of illuminating spaces occupied by humans, since there are adverse health effects of over-illumination by artificial lights or by mismatch of natural light sources. Colour rendering index, or CRI, is a measure of the quality of colour light, devised by the International Commission on Illumination (CIE). ... The CIE 1931 color space chromaticity diagram with wavelengths in nanometers. ... Colour rendering index, or CRI, is a measure of the quality of colour light, devised by the International Commission on Illumination (CIE). ... This cosmetics store has lighting levels over twice recommended levels and sufficient to trigger headaches and other health effects Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity. ...


Spectral power distribution plot

The spectral power distributions provided by many manufacturers may have been produced using 10 nanometre increments or more on their spectroradiometer.[citation needed] The result is what would seem to be a smoother (fuller spectrum) power distribution than the lamp actually has. Increments of 2 nm are mandatory[citation needed] for taking measurements of fluorescent lights. Here is an example of just how different an incandescent lamp's SPD graphs compared to a fluorescent lamp. incandescent and fluorescent Spectral Power Distributions File links The following pages link to this file: Color temperature Spectral density Spectrophotometry Spectroradiometer Categories: GFDL images ... The spectral power distribution (SPD) of a light source is a measurement of the energy output at points (usually 31) along the visible spectrum. ... A nanometre (American spelling: nanometer, symbol nm) is a unit of length in the metric system, equal to one thousand-millionth of a metre, which is the current SI base unit of length. ... Spectroradiometers, (aka - spectraradiometer) which operate almost like the visible region spectrophotometers are designed to measure the spectral power distributions of illuminants in order to evaluate and catagorize lighting for sales by the manufacturer or for the customers to confirm the lamp they decided to purchase is within their specifications. ...


See also

Luminous efficacy is a property of light sources, which indicates what portion of the emitted electromagnetic radiation is usable for human vision. ... This cosmetics store has lighting levels over twice recommended levels and sufficient to trigger headaches and other health effects Over-illumination is the presence of lighting intensity (illuminance) beyond that required for a specified activity. ... In photography and image processing, color balance (sometimes gray balance, neutral balance, or white balance) refers to the adjustment of the relative amounts of red, green, and blue primary colors in an image such that neutral colors are reproduced correctly. ... Brightness temperature is a measure of the intensity of radiation thermally emitted by an object, given in units of temperature because there is a correlation between the intensity of the radiation emitted and physical temperature of the radiating body which is given by the Stefan-Boltzmann law. ... Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. ...

References

  1. Berns, Roy S. (2000). Billmeyer and Saltzman's Principles of Color Technology, 3rd edition, New York: Wiley. ISBN 0-471-19459-X. 
  2. Stroebel, Leslie; John Compton; Ira Current; Richard Zakia (2000). Basic Photographic Materials and Processes, 2nd edition, Boston: Focal Press. ISBN 0-240-80405-8. 
  3. Wyszecki, Günther; W. S. Stiles (1982). Color Science Concept and Methods, Quantitative Data and Formulae. New York: Wiley. ISBN 0-471-02106-7. 

External links

Film- and video-related


  Results from FactBites:
 
Olympus Microscopy Resource Center: Light and Color - Color Temperature: Interactive Java Tutorial (708 words)
The concept of color temperature is based on the relationship between the temperature and radiation emitted by a theoretical standardized material, termed a fl body radiator, cooled down to a state in which all molecular motion has ceased.
Color changes are first apparent as the pot begins to glow a dull red when heated to a temperature above 900 K. As the temperature is increased to a range between 1,500 K and 2,000 K, the pot turns from yellowish to brighter red in color.
Increasing the temperature even further, to a range above 3,000 K, transforms the color to a yellow-white (the color temperature of a tungsten filament), and at 5,000 K and above, a bluish-white color appears at the base of the pot (the color temperature of daylight).
  More results at FactBites »

 
 

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