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Kelvin scale

Measuring the temperature of color in light.


Color temperatures of various light sources
Color temperatures of various light sources

The light spectrum is scientifically described in terms of color temperature. It is measured in degrees Kelvin (°K).

HOW COLOR TEMPERATURE IS MEASURED

A material or an object (usually termed a "black body") that is heated in a vacuum will begin to glow and it will glow in different colors depending upon how much it is heated.

As the heat of the material increases, causing it to undergo color change, each different color of the spectrum is reached and the temperature of the material is measured in degrees Celsius (or centigrade). By adding 273 to the Celsius temperature, you are able to express the color temperature in degrees Kelvin (°K).

As incrementally greater amounts of heat are applied to the material, thereby gradually increasing its temperature, its color changes from black to what we perceive as “warm” colors (the red and yellow the material emanates), then to what we commonly call “cooler” colors. Blue is actually hotter than red, although blue is generally described as a "cool" color. Thus, 10,000K light has a lot of blue in it while 2,000K light leans towards red and yellow.

COLOR TEMPERATURES OF LIGHT SOURCES

The table on the left shows the color temperatures in degrees Kelvin of various light sources.


THREE COLOR TEMPERATURE STANDARDS

Photographers use three standard light color temperatures. The first is called "daylight" for natural outdoors light, while the other two are incandescent (artificial light) color temperature standards:
- 5500K (daylight)
- 3200K (tungsten studio lamps) and
- 3400K (photo lamps or photofloods).

DAYLIGHT FILM

Daylight film is color-balanced so that it will produce realistic-looking color from a 5500K light source – the average light around mid-day. This same color of light is more or less produced by electronic flash and blue flash bulbs. Digital cameras have their white balance preset for daylight photography.

Daylight film is color-balanced for the average exterior light around mid-day. A digital camera's white balance is preset for daylight.
Daylight film is color-balanced for the average exterior light around mid-day. A digital camera's white balance is preset for daylight.

Artificial lighting is the reason for a
Artificial lighting is the reason for a "warm" color cast when using daylight film or a daylight White Balance setting.

COLOR SHIFT

If daylight film, or a digital camera's white balance setting for daylight, is used in artificial lighting (tungsten bulbs or fluorescent tubes), it will have a strong overall color cast of either red (from the incandescent lights) or green (from the fluorescent light). This is known as “color shift.” Color-balancing filters can be placed in front of the lens or the light source to correct the light temperature so that daylight film will render the light with a more natural look. (See our section on Filters.)

Film that is color-balanced for use with floodlamps as the light source will also exhibit a color shift (a bluish cast) when used in daylight. This can be corrected through the use of an 85B (amber-tinted) filter.

A digital camera's white balance can be changed to compensate for variations in the color of the light source or to deliberately introduce a "warm" or "cold" color cast into a picture.


You may be wondering: Is there a meter to measure color temperature?

The answer is yes, indeed.

Color temperature readings are taken on a color temperature meter, sometimes just called a "color meter."

It is employed by photographers to determine what filters or camera or lens settings are required for a desired color effect.

The particular color meter shown on the right currently retails for just under $1,300. Really! There are several other models available at different prices, but most, especially the good ones, are expensive.

Kenko KCM-3100 Color Temperature and Filtration Meter.
Kenko KCM-3100 Color Temperature and Filtration Meter.