Light has different color temperatures throughout the day, and white balance is the process of removing the color casts that different color temperatures produce. The human eye is much better at processing color, and we can always see what should be white in an image. But a camera needs help!
As I mentioned above, different times of day create different color temperatures. Light is measured in kelvins, and neutral light is produced at 5000 k (kelvins). The following list gives you a guide to the different temperatures produced by different sorts of light.
- 1000-2000k: Candlelight
- 2500-3500k: Tungsten Light (Normal household bulb)
- 3000-4000k: Sunrise / Sunset (Clear skies)
- 4000-5000k: Fluorescent Light
- 5000-5500k: Electronic Flash
- 5000-6500k: Daylight (Clear skies with sun overhead)
- 6500-8000k: Overcast skies (Moderate)
- 9000-10000k: Heavily overcast skies or shade
White Balance Modes
If you look at my chart of symbols, you'll probably recognize them from your DSLR. The first three symbols allow for a range of color temperatures. Auto White Balance (AWB) has advanced greatly in reliability, and it will set the color temperature correctly in all but the most complicated lighting situations nowadays. Custom White Balance allows users to set their own white balance using a gray card (which gives a shot with 18% gray, which is the midpoint between true black and true white). This is often used by professional photographers in a studio environment where it is often absolutely vital to have an exactly white background.
The Kelvin setting allows you to set the color temperature at will, giving a very precise result, as you can tweak the kelvins in small increments.
The rest of the symbols relate to the different color temperatures noted above. It should be noted that tungsten light produces an orange cast on images, while fluorescent light produces a green tinge.
Tips for Using White Balance
As I stated, you can rely on AWB quite a lot of the time. This is particularly true if you are using an external light source (such as a flashgun), as the neutral light emitted by this will usually cancel out any color casts. Some subjects can cause a problem for AWB, though -- in particular, photos that have a natural abundance of warmth or coolness. The camera can misinterpret these subjects as casting a color cast over an image, and the AWB will try to adjust accordingly. So, for instance, with a subject that has an overabundance of warmth, the camera will cast a blueish tinge over the image in an attempt to balance this out. Of course, all this does is leave your camera with a funny color cast!
Another confusing thing for AWB in cameras is mixed lighting (such as where an image has a mixture of ambient and artificial lighting). In general, it's best to manually set the white balance for the ambient lighting, which will give everything lit by ambient lighting a warm tone. Warm tones tend to be more attractive to the eye than the very cold and sterile cool tones.
The white balance feature in DSLRs takes away the need for expensive filters to correct color casts, and it allows for precise alterations and extremely accurate color temperature readings. Understanding the different modes will also help you to correct any mistakes that AWB might make.