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Color temperature is measured in Kelvins (K) and equals the temperature of the ideal black body radiating the same spectrum. There are three commonly used values. Printing and photography often involves 5500K temperature (this value was introduced by folks from Kodak under the name of “daylight”. There is a joke that in the real world this value is the color temperature of midday sunlight near the offices of this company). For computer-processed images a color temperature 6500K is used (it corresponds to bright sunlight in a clear sky, while a slightly clouded sky has a color temperature of 6500-7000K). Sometimes, but quite rarely, the color temperature is set to 9300K giving out a slight bluish hue (an analog from nature – it is the color temperature of a thin shadow on a bright day).

Talking about artificial light sources, the ordinary bulb has a color temperature of about 2000K, powerful studio incandescent lamps and daylight lamps with “warm” phosphors – about 3000K, daylight lamps with “cold” phosphors – 4000K.

The aforementioned sRGB standard recommends a color temperature of 6500K (D65), and this is the default temperature of many computer monitors. But still, the color temperature of LCD monitors has some specific features. First, as I mentioned above, color temperature may vary considerably between different tones of gray. On a well-calibrated monitor the temperatures of white and 50% gray differ by a score or two of degrees, but for the majority of monitors this difference is as high as 500K and more (up to a thousand degrees for high temperatures). It means that if white looks really white, light-gray will look bluish (it is the temperature of gray that’s usually higher, but there are exceptions, too).

Second, CRT monitors allow adjusting the color temperature rather smoothly along the entire range, from 5000K to 9300K, with a stepping of 50..100K, but LCD monitors usually have three or four temperature values for the user to select among them. For a smooth adjustment of the temperature, you can only use the independent controls for the three basic colors (R, G and B), which is rather unhandy and requires much experience to achieve an appropriate result.

Moreover, the temperature of a CRT monitor is usually changed very neatly, while LCD monitors may produce some artifacts at different temperatures. For example, at a reduced temperature, the screen gets a strong pinkish or greenish hue. On a temperature increase, gray color may become so bluish that the calibrator just can’t measure its temperature…

One more parameter that slightly affects the quality of color reproduction is the so-called gamut range. It is a known fact that the human eye perceives light with wavelengths from 390nm to 760nm, different wavelengths being different colors from violet to red. Display devices, however, reproduce a much narrower range of colors.

 
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