Understanding Color Temperature

While professional photographers will speak about the coolness (blueness) or warmth (reddishness) of light, they must be more precise when they are setting up a professional photo shoot. That's when they take out their color temperature meter or colorimeter and measure the temperature of light falling on their subject. Color temperature is measured in degrees Kelvin (K).

In the mid-nineteenth century, Lord Kelvin sought to establish a temperature scale that would have no negative values. Therefore, the Kelvin scale begins at absolute zero, below which molecular energy ceases. But what are important to photographers are Lord Kelvin's experiments with heating a carbon rod to such high temperatures that it changed colors, becoming red hot and then blue. It is this correlation of color to temperature that is the basis of the photographer's color temperature meter.

5,000°Kto 5,500°K is generally considered to be daylight. However, as we mentioned earlier in the chapter, daylight fluctuates. So, 5,000°Kto 5,500°K is an idealized value of daylight at midday in June in the temperate zone of the northern hemisphere, rather than a true, constant value. Real daylight (which is a combination of sunlight and ambient skylight) can measure anywhere from about 2,000°Kto

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