Color Temperature...

Color temperature is the temperature in degrees Kelvin of a black body (light emitted from a source), heated to produce a certain color of light. It is a way to describe how blue or red a light source is. For example, candlelight, which has a color temperature of around 2000K, is towards the red end of the scale and is considered a warm(reddish) light source. Sunlight at noon measures out at about 5500K, and is much colder(bluer) than candlelight. If you have ever observed a campfire you may have noticed that the new flames coming off of a piece of wood are generally reddish, while the coals deep in the fire tend to produce a more bluish flame, this happens because the coals burn at a higher temperature than the fresh burning wood.

Here's a basic diagram that illustrates color temperature and it's effect on color images. As you move your mouse cursor over any of the four images below, the scale to the left will indicate the approximate color temperature for that scene. These images were photographed with a digital camera set to record at 5500 Kelvin. If you were to try this same test with a digital camera set to auto white balance, your camera would automatically correct the images and try to give them all a neutral white balance (make them look the same).

Does the color of the apple and banana change as the color temperature of the light they are viewed under changes from warm to cold? How would a change in color temperature effect your ability to assess the color of a digital inkjet print?

A basic understanding of color temperature is necessary to properly assess and manage color. It is impossible to manage color under incorrect lighting conditions, especially prints.

One last item about color and color perception. There is this nasty little term called Metamerism that many of you may have already heard of. You've most likely heard it mentioned in regards to digital image output, specifically ink jet printers. Metamerism is a condition, where two samples with different spectral qualities look the same under different lighting conditions, IE: color temperatures.

The more important term to grasp here is metamers. Metamers are two color samples that look different under different lighting conditions. For example, you make an inkjet print that looks great (color wise) under tungsten lamps but when you view it outdoors under daylight conditions it seems to exhibit an unwanted color cast, view the print under tungsten lights and it looks fine again. Our eye interprets the same ink on paper differently dependent on the lighting condition, namely color temperature.

Color temperature and metamerism are important terms to understand and consider in a color managed workflow. The next color topic we are going to explore is Color Models.

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