Information about Color Temperature
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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
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 kelvins, 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.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.
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.
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 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.
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Increasing hues of the Planckian locus
The colors shown are approximate and symbolic, not colorimetrically accurate. A colorimetrically-accurate diagram is 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)
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.
"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).
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).
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.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.
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.
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:5000 K (D50), 5500 K (D55), 6500 K (D65), 7500 K (D75) and 9300 K.
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.
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.
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.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
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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.
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.
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.
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. |
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.
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.
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
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.
Spectral power distribution plot
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The spectral power distributions provided by many manufacturers may have been produced using 10 nanometre increments or more on their spectroradiometer. 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 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.
See also
References
- Berns, Roy S. (2000). Billmeyer and Saltzman's Principles of Color Technology, 3rd edition, New York: Wiley. ISBN 0-471-19459-X.
- Stroebel, Leslie; John Compton; Ira Current; Richard Zakia (2000). Basic Photographic Materials and Processes, 2nd edition, Boston: Focal Press. ISBN 0-240-80405-8.
- 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
- Charles Poynton's Color FAQ for the basics.
- Frequently asked questions about Color Physics - also includes history of the CIE color specification
- What color is a blackbody? - Colorimetrically-calculated blackbody RGB color values and comment
- Color-temperature: visualising blackbody radiation - Blackbody curves for typical lightsources, and colorimetrically-calculated blackbody color strip
- Specifying Color GE's "Learn About Light" pages
Film- and video-related
- White Balance - Intro at nikondigital.org
- Understanding White Balance - Tutorial
- White Balance - Understanding its use in digital photography
visible spectrum (or sometimes 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.
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Chromaticity is the quality of a color as determined by its purity and hue.[1]
"Purity" in this context, called "colorfulness" in CIECAM02, and "chroma" in Munsell, can be measured as the distance of a color from the neutral axis in a color space such as CIE
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"Purity" in this context, called "colorfulness" in CIECAM02, and "chroma" in Munsell, can be measured as the distance of a color from the neutral axis in a color space such as CIE
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black body is an object that absorbs all electromagnetic radiation that falls onto it. No radiation passes through it and none is reflected. It is this lack of both transmission and reflection to which the name refers.
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The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero — the coldest possible temperature — is zero kelvins
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For a general introduction, see black body.
In physics, Planck's law describes the spectral radiance of electromagnetic radiation at all wavelengths from a black body at temperature .
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In physics, Planck's law describes the spectral radiance of electromagnetic radiation at all wavelengths from a black body at temperature .
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black body is an object that absorbs all electromagnetic radiation that falls onto it. No radiation passes through it and none is reflected. It is this lack of both transmission and reflection to which the name refers.
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William Thomson, 1st Baron Kelvin, OM, GCVO, PC, PRS, FRSE, (26 June 1824 – 17 December 1907) was a British mathematical physicist, engineer, and outstanding leader in the physical sciences of the 19th century.
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Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing
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incandescent light bulb (also spelled lightbulb) or incandescent lamp is a source of artificial light that works by incandescence. An electrical current passes through a thin filament, heating it until it produces light.
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fluorescent lamp is a gas-discharge lamp that uses electricity to excite mercury vapor in argon or neon gas, resulting in a plasma that produces short-wave ultraviolet light. This light then causes a phosphor to fluoresce, producing visible light.
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For a general introduction, see black body.
In physics, Planck's law describes the spectral radiance of electromagnetic radiation at all wavelengths from a black body at temperature .
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In physics, Planck's law describes the spectral radiance of electromagnetic radiation at all wavelengths from a black body at temperature .
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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. The nervous system derives color by comparing the responses to light from the several types of cone photoreceptors in the eye.
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The Sun
Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for
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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.
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Star
The effective temperature of a star is the temperature of a black body with the same luminosity per surface area () as the star and is defined according to the Stefan-Boltzmann law ...... Click the link for more information.
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. It can occur when light travels in transparent solids and liquids, but is most prominently seen in gases.
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Fire is an oxidation process that releases energy in varying intensities in the form of light (with wavelengths also outside the visual spectrum) and heat and often creates smoke. It is commonly used to describe either a fuel in a state of combustion (e.g.
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A white point is a set of tristimulus values or chromaticity coordinates that serve to define the color "white" in image capture or reproduction. Depending on the application, different definitions of white are needed to give acceptable results.
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Degrees of freedom is a general term used in explaining dependence on parameters, and implying the possibility of counting the number of those parameters.
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Degrees of freedom in mechanics (physics)
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Photography [fә'tɑgrәfi:],[foʊ'tɑgrәfi:] is the process of recording pictures by means of capturing light on a light-sensitive medium, such as a film or electronic sensor.
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Derived from the term micro reciprocal degree, the mired (M) is a unit of measurement used to express color temperature; it is equivalent to 10−6 K−1 or MK−1, and is given by the formula:
where M
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where M
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Derived from the term micro reciprocal degree, the mired (M) is a unit of measurement used to express color temperature; it is equivalent to 10−6 K−1 or MK−1, and is given by the formula:
where M
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where M
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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.
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Tungsten film is designed to give accurate colors under tungsten light. The majority of color film is balanced for daylight (direct light from the sun), or for use with electronic flash. It was developed for photographers who use the tungsten lights, also known as photofloods.
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Incandescence is the release of thermal radiation from a body due to its temperature. The distribution of energy emissions across the electromagnetic spectrum is described by Planck's law; at temperatures occurring on Earth, the release of radiation is usually predominantly in the
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6, 5, 4, 3, 2, 1, 0, −1
(mildly acidic oxide)
Electronegativity 2.36 (scale Pauling)
Ionization energies 1st: 770 kJ/mol
2nd: 1700 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.
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(mildly acidic oxide)
Electronegativity 2.36 (scale Pauling)
Ionization energies 1st: 770 kJ/mol
2nd: 1700 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.
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filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or rectangle shape mounted in a holder accessory, or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which can be screwed in
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color gel or color filter (UK colour gel or colour 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
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