This is not a technical article. Rather, consider this a practical approach to the concept of White Balance and, specifically, Kelvin White Balance. Kelvin White Balance (identified on EOS cameras with an icon with the letter "K" in it) is available on nearly all Canon EOS SLRs, except for EOS Rebel models.
Understanding Light and Color Temperatures
If one looks at the same object under different lighting situations, there is the perception that the object has the same color in each lighting scenario. For example, a red apple always appears red in the kitchen, at the office and at a picnic, despite the different lighting conditions. The human brain is so powerful that it instantly and constantly remaps colors so that things, like the apple, look the way they should in the mind’s eye. In our brain, this effect is called “chromatic adaptation,” or color constancy. However, this setup is far from true for digital sensors. A red apple photographed under different light sources will be captured as having different shades of red or even different colors. When the correction occurs in a camera, it is referred to as “White Balance.”
When Automatic White Balance (AWB) is in effect, the camera's processor analyzes the overall color of the image and removes the color cast from neutral or white parts of an image. This works very well under normal daylight conditions, but a problem arises when the scene is dominated by one color or if there is no obvious natural white present in the image.
The light from sunlight, electronic flash and even traditional household light bulbs varies in color, and these variations can be defined by "color temperature." Color temperature is measured in degrees Kelvin (°K). As you can see on this graph, the lower temperatures are on the yellow end of the scale, which we generally consider “warm,” and the higher values are on the blue end of the scale, which we generally consider “cool.”
Auto White Balance and White Balance Presets
Automatic White Balance (AWB) assesses and automatically shifts overall white balance to try to capture images that are neutral in color. Canon EOS Digital SLRs adjust white balance over a range of roughly 3000 to 7000 degrees Kelvin, when set to AWB. As a reference, the color temperature of candlelight is around 1,900°K, mid-day sun is around 5,500°K, a cloudy sky comes in around 6,000°K and deep shade on a clear day can be 7000°K or higher.
Another option is to use one of the preset White Balance choices and lock it in yourself for the light you're working in, rather than having the camera automatically set White Balance.. For “Incandescent” the color temperature is normally around 3,000°K, for “Fluorescent” it is 4,200°K, for “Flash” it is set at approximately 5,400°K and “Shade” is somewhere in between 7,000°K and 8,000°K.
Something interesting to know is that the Kelvin color temperature scale only deals with blue and amber, not with magenta or green. Because of this, it is best to use this feature under daylight or tungsten lighting situations, as it does not work as well under fluorescent lighting conditions. Images shot using Auto White Balance show different "moods" than images shot using White Balance presets.
The Kelvin White Balance option
The Kelvin (K) White Balance setting is one many photographers hesitate to use, but can be a great option to be familiar with. By dialing in a Kelvin temperature, you assign a look to the overall color, based on the lighting in the scene. Kelvin White Balance offers fine control of the overall warmth or coolness of color, since the settings are set in very small 100°K increments on EOS cameras. In daylight, setting a higher Kelvin value, such as 5,500°K or 7,500°K, introduces a deliberate amber tone to the image that can mimic the look of late-afternoon sunlight. And a lower Kelvin value, such as 3,500°K or even 2,500°K, progressively adds a cool blue hue to the overall scene.
Matching the Kelvin setting to the type of daylight or tungsten-type artificial light in a scene to get white balance as close to perfect as possible is one way to use the Kelvin White Balance option. Another is to vary the K-value to make subtle or major changes, such as the intentional warming of daylight just mentioned. With RAW images, it's always possible to experiment and fine-tune the Kelvin value at the computer until you get just what you're looking for or get acquainted with the possibilities of Kelvin White Balance. And when recording video or shooting JPEG original images with EOS Digital SLRs, the Kelvin White Balance setting becomes a great way to nail down a particular color or "look" in any daylight-type lighting condition or under tungsten artificial lighting. Of course, with video or JPEG imagery, white balance can't simply be reset later on in the computer -- one reason that the fine control of the Kelvin White Balance setting can sometimes be such an important asset.
If the Auto White Balance or Daylight White Balance isn't quite giving you the look you want, Kelvin White Balance becomes an option worth pursuing.
To get initially acquainted with the Kelvin White Balance setting, you might want to take three images (JPEGs or even short video clips will be fine for this purpose) in a specific lighting condition -- such as sunlight or an overcast sky. Set the Kelvin White Balance option and on your camera's Shooting Menu, dial-in a standard daylight Kelvin value like 5,500°K. Be sure to lock it in by pressing the "SET" button on the back of the camera.
Then, repeat, with the K-value set at its highest setting (10,000°K). You'll see how much more amber is introduced into the white balance. After that, reset the Kelvin value to its lowest setting (2,500°K) and observe the difference. Often, you'll be making adjustments in far smaller increments for subtle changes. But this is an easy way to see how Kelvin White Balance can warm up or cool down the lighting in a scene.
A single scene can have very different artistic interpretations simply by modifying the color temperature. If your images feel a bit too warm or too cool, or they don’t represent the vision that you are trying to achieve, White Balance and Kelvin settings are great technical and creative tools in your photo arsenal.