What Is Color Temperature?

mainWait a minute, isn’t “temperature” associated with weather? How can color have temperature? The thing is that color temperature is actually a characteristic of visible light that has several important applications in photography, publishing, and many other fields. We actually see and feel it all the time, it’s just that we don’t realize that we like certain color temperatures more than others. The concept of color is more easily apparent to us. We can see what’s red and what’s blue. There are a lot of characteristics of color that we feel, but don’t realize. So what exactly is color temperature?  

First of all, how is temperature related to color?

marblesLet’s consider an object, say a marble. For the sake of this discussion, let’s assume that it is a perfectly black marble. It’s black because it absorbs all lights equally: green, blue, red, everything. Some objects appear red because they absorb everything except red. The red color gets reflected and we perceive the object to be of red color. That’s how we see colors. Anyway, coming back to our marble. If you were to heat it, it would, in theory, emit all frequencies of light equally. In case you didn’t know, white light consists of all the different colors and each color has it’s own frequency. It is this property that makes each color unique.

Now if we raise the temperature of the marble to, say 2000 degrees Fahrenheit, and it will become all red. If you have an electric stove, you would have seen this. As the coils warm up, they glow red. If you were to increase the temperature even further, to say 10,000 degrees Fahrenheit, it would appear white. Keep going, past 17,000 degrees, it would look blue. You see where we are going with this? As the temperature increases, it keeps changing its color. So the color temperature refers to the temperature that an object must be heated to in order to get that color. This marble is of course an example of an ideal blackbody radiator. These objects don’t exist in reality. Graphite comes pretty close, but it is still not a perfect black body radiator.

How do we measure it?

thermometerColor temperature is measured on the Kelvin scale. Kelvin, like Fahrenheit and Centigrade, is a scale for measuring temperature. Zero degrees Kelvin (which is defined as ‘absolute zero’ where there is no molecular movement) corresponds to -459.67 degrees Fahrenheit. The relationship between color and Kelvin temperature is derived from heating a “blackbody radiator” until it glows. The particular color seen at a specific temperature is the color temperature. When the blackbody is hot enough and begins to emit light, it is dull red. As more heat is applied, it glows yellow, and then white, and ultimately blue.

One interesting thing to note is that when an object has a higher color temperature, it is referred to as looking “cooler” due to its bluish nature. Conversely, an object with a lower color temperature is called “warmer” due to its reddish hue. You can see this with
light bulbs.

Color Temperature in Photography

The concept of color temperature is used extensively in photography. Let’s consider the camera flash. For example, the color of the light emitted by a flash is rated at 5500 degrees; it is designed to imitate noon daylight. If the flash produces light that is 6000 degrees Kelvin, it has a slight bluish tinge. If it is rated at 4800 degrees, it is slightly warmer, or more yellowish, than white light. This is used a lot by photographers to get spectacular visual effects. It’s not just the software on the camera that helps us capture wonderful pictures, you also need to know what properties to change. For example, when a cloud cover has obscured the sun during the middle of the day, some of the red and yellow wave lengths of light are absorbed by the minute water droplets of the clouds. The colder end of the spectrum, the bluish wave lengths, pass through unimpeded.

Digital technology uses these traditional concepts but with a new twist. You can simply adjust your white point to change the color balance. For example, if you lower the white point to, say, 3200, you are telling the camera that you want yellowish light to be shown as white noon-type daylight. This means that daylight and flash (5500K) will be bluish, and overcast conditions and shade (about 7500K) will be exceptionally blue. Intricate knowledge of things like these separates the DSLR-point-and-click-amateurs from professional photographers who capture those gorgeous pictures we see on the web.

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One thought on “What Is Color Temperature?

  1. Pingback: Kruithof Curve | Perpetual Enigma

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