Color temperature
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Color temperature is a parameter describing the color of a
Color temperature has applications in
Color temperatures over 5000 K are called "cool colors" (bluish), while lower color temperatures (2700–3000 K) are called "warm colors" (yellowish). "Warm" in this context is with respect to a traditional categorization of colors, not a reference to black body temperature. The hue-heat hypothesis states that low color temperatures will feel warmer while higher color temperatures will feel cooler. The spectral peak of warm-colored light is closer to infrared, and most natural warm-colored light sources emit significant infrared radiation. The fact that "warm" lighting in this sense actually has a "cooler" color temperature often leads to confusion.[1]
Categorizing different lighting
Temperature | Source |
---|---|
1700 K | Match flame, low pressure sodium lamps (LPS/SOX) |
1850 K | Candle flame, sunset/sunrise |
2400 K | Standard incandescent lamps |
2550 K | Soft white incandescent lamps |
2700 K | "Soft white" compact fluorescent and LED lamps |
3000 K | Warm white compact fluorescent and LED lamps |
3200 K | Studio lamps, photofloods, etc. |
3350 K | Studio "CP" light |
5000 K | Horizon compact fluorescent lamps (CFL)
|
5500–6000 K | Vertical daylight, electronic flash
|
6200 K | Xenon short-arc lamp[2] |
6500 K | Daylight, overcast |
6500–9500 K | LCD or CRT screen
|
15,000–27,000 K | Clear blue poleward sky |
The color temperature of the electromagnetic radiation emitted from an ideal black body is defined as its surface temperature in kelvins, or alternatively in micro reciprocal degrees (mired).[3] This permits the definition of a standard by which light sources are compared.
To the extent that a hot surface emits
Many other light sources, such as
The Sun
The Sun closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is 5772 K.[4] The color temperature of sunlight above the atmosphere is about 5900 K.[5]
The Sun may appear red, orange, yellow, or white from Earth, depending on
Some
Daylight has a spectrum similar to that of a black body with a correlated color temperature of 6500 K (
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".[6]
Applications
Lighting
For lighting building interiors, it is often important to take into account the color temperature of illumination. A warmer (i.e., a lower color temperature) light is often used in public areas to promote relaxation, while a cooler (higher color temperature) light is used to enhance concentration, for example in schools and offices.[7]
CCT dimming for LED technology is regarded as a difficult task, since binning, age and temperature drift effects of LEDs change the actual color value output. Here feedback loop systems are used, for example with color sensors, to actively monitor and control the color output of multiple color mixing LEDs.[8]
Aquaculture
In fishkeeping, color temperature has different functions and foci in the various branches.
- In freshwater aquaria, color temperature is generally of concern only for producing a more attractive display.[citation needed] Lights tend to be designed to produce an attractive spectrum, sometimes with secondary attention paid to keeping the plants in the aquaria alive.
- In a saltwater/reef aquarium, color temperature is an essential part of tank health. Within about 400 to 3000 nanometers, light of shorter wavelength can penetrate deeper into water than longer wavelengths,[9][10][11] providing essential energy sources to the algae hosted in (and sustaining) coral. This is equivalent to an increase of color temperature with water depth in this spectral range. Because coral typically live in shallow water and receive intense, direct tropical sunlight, the focus was once on simulating this situation with 6500 K lights.
Digital photography
In digital photography, the term color temperature sometimes refers to remapping of color values to simulate variations in ambient color temperature. Most digital cameras and raw image software provide presets simulating specific ambient values (e.g., sunny, cloudy, tungsten, etc.) while others allow explicit entry of white balance values in kelvins. These settings vary color values along the blue–yellow axis, while some software includes additional controls (sometimes labeled "tint") adding the magenta–green axis, and are to some extent arbitrary and a matter of artistic interpretation.[12]
Photographic film
Photographic emulsion film does not respond to lighting color identically to the human retina or visual perception. An object that appears to the observer to be white may turn out to be very blue or orange in a photograph. The color balance may need to be corrected during printing to achieve a neutral color print. The extent of this correction is limited since color film normally has three layers sensitive to different colors and when used under the "wrong" light source, every layer may not respond proportionally, giving odd color casts in the shadows, although the mid-tones may have been correctly white-balanced under the enlarger. Light sources with discontinuous spectra, such as fluorescent tubes, cannot be fully corrected in printing either, since one of the layers may barely have recorded an image at all.
Photographic 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 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 lamps will appear as white (3200 K) in the photograph. Color negative film is almost always daylight-balanced, since it is assumed that color can be adjusted in printing (with limitations, see above). Color transparency film, being the final artefact in the process, has to be matched to the light source or filters must be used to correct color.
If there is more than one light source with varied color temperatures, one way to balance the color is to use daylight film and place color-correcting gel filters over each light source.
Photographers sometimes use color temperature meters. These are usually designed to read only two regions along the visible spectrum (red and blue); more expensive ones read three regions (red, green, and blue). However, they are ineffective with sources such as fluorescent or discharge lamps, whose light varies in color and may be harder to correct for. Because this light is often greenish, a magenta filter may correct it. More sophisticated colorimetry tools can be used if such meters are lacking.[13]
Desktop publishing
In the desktop publishing industry, it is important to know a monitor's color temperature. Color matching software, such as Apple's
- 5000 K (CIE D50)
- 5500 K (CIE D55)
- 6500 K (D65)
- 7500 K (CIE D75)
- 9300 K
D50 is scientific shorthand for a standard illuminant: the daylight spectrum at a correlated color temperature of 5000 K. Similar definitions exist for D55, D65 and D75. Designations such as D50 are used to help 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.
TV, video, and digital still cameras
The
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. Most cameras also have an automatic white balance function that attempts to determine the color of the light and correct accordingly. While these settings were once unreliable, they are much improved in today's digital cameras and produce an accurate white balance in a wide variety of lighting situations.
Artistic application via control of color temperature
Video camera operators can white-balance objects that are not 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 that is light blue, such as faded blue denim; in this way white-balancing can replace a filter or lighting gel when those are not available.
Cinematographers do not "white balance" in the same way as video camera operators; they 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. Cinematographers also work closely with set designers and lighting crews to achieve the desired color effects.[14]
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". Note that this sense of temperature is the reverse of that of real temperature; bluer is described as "cooler" even though it corresponds to a higher-temperature black body.
"Warm" gray | "Cool" gray |
Mixed with 6% yellow | Mixed with 6% blue |
Color rendering index
The CIE color rendering index (CRI) is a method to determine how well a light source's illumination of eight sample patches compares to the illumination provided by a reference source. Cited together, the CRI and CCT give a numerical estimate of what reference (ideal) light source best approximates a particular artificial light, and what the difference is.
Spectral power distribution
Light sources and illuminants may be characterized by their
Color temperature in astronomy
In
For most applications in astronomy (e.g., to place a star on the HR diagram or to determine the temperature of a model flux fitting an observed spectrum) the effective temperature is the quantity of interest. Various color-effective temperature relations exist in the literature. There relations also have smaller dependencies on other stellar parameters, such as the stellar metallicity and surface gravity[19]
See also
- Brightness temperature
- Color balance
- Effective temperature
- Kruithof curve
- Luminous efficacy
- Color metamerism
- Colored fire
- Overillumination
- Whiteness
References
- ^ See the comments section of this LightNowBlog.com article Archived 2017-03-07 at the Wayback Machine on the recommendations of the American Medical Association to prefer LED-lighting with cooler color temperatures (i.e. warmer color).
- ^ "OSRAM SYVLANIA XBO" (PDF). Archived from the original (PDF) on March 3, 2016."
- ^ Wallace Roberts Stevens (1951). Principles of Lighting. Constable.
- ^ Williams, David R. (2022). "Sun Fact Sheet". NASA. Archived from the original on March 16, 2023. Retrieved March 24, 2023.
- ^ "Principles of Remote Sensing". CRISP. Archived from the original on July 2, 2012. Retrieved June 18, 2012.
- ^
Chris George (2008). Mastering Digital Flash Photography: The Complete Reference Guide. ISBN 978-1-60059-209-6.
- ]
- ISSN 1993-890X. Archived from the originalon April 29, 2014.
- ^ Chaplin, Martin. "Water Absorption Spectrum". Archived from the original on July 17, 2012. Retrieved August 1, 2012.
- S2CID 11061625.
- ISBN 0-444-41490-8. Archivedfrom the original on December 21, 2017. Retrieved August 1, 2012.
- ^ Kern, Chris. "Reality Check: Ambiguity and Ambivalence in Digital Color Photography". Archived from the original on July 22, 2011. Retrieved March 11, 2011.
- ^ ISBN 978-2-940447-55-8.
- ISBN 978-1-317-35927-2.
- ISBN 3900734070)
- doi:10.1002/col.1065. Archived from the originalon February 5, 2009.
- ^ Gretag's SpectroLino Archived 2006-11-10 at the Wayback Machine and X-Rite's ColorMunki Archived 2009-02-05 at the Wayback Machine have an optical resolution of 10 nm.
- ISBN 3-540-64165-3.
- .
Further reading
- Stroebel, Leslie; John Compton; Ira Current; Richard Zakia (2000). Basic Photographic Materials and Processes (2nd ed.). Boston: Focal Press. ISBN 0-240-80405-8.
- Wyszecki, Günter; Stiles, Walter Stanley (1982). "3.11: Distribution Temperature, Color Temperature, and Correlated Color Temperature". Color Science: Concept and Methods, Quantitative Data and Formulæ. New York: Wiley. pp. 224–229. ISBN 0-471-02106-7.
External links
- Kelvin to RGB calculator from Academo.org
- Boyd, Andrew. Kelvin temperature in photography at The Discerning Photographer.
- Charity, Mitchell. What color is a black body? sRGB values corresponding to blackbodies of varying temperature.
- Lindbloom, Bruce. ANSI C implementation of Robertson's method to calculate the correlated color temperature of a color in XYZ.
- Konica Minolta Sensing. The Language of Light.