Simply talking, we can say that White Balance is that thing you have to properly set in the camera to have the real colors! If you want an extensive technical explanation, go to the wiki.
So white balance is just a method to find the right color balance. That means “understand when white is white” and from that point, understand the real color of things in the image. The automatic white balance (AWB) in almost every digital camera, does not match 100% the colors and sometimes we have to specify what kind of light we are exposing the picture.
What kind of light? Light is just light! Different light sources produce different temperature lights. For example, the light in a cloudy day is totally different from the direct light of a sunny day or from the light of an electric neon tube. The colors render differently and our eyes and brain adjust automatically to that light to show us colors as much close as possible to the original.
An image will clarify this better.
These two images have been taken the same day, at the same time. I just changed the white balance. The first one, told the camera to adjust to a light temperature that didn’t match with the light in that moment. Let’s think about light from a non-technical point of view. Light comes from one or multiple sources and it reflects all around. Objects absorbed some portion of that light and reflect some other portion of it. The reflected light is the color of the objects. Depending on the light source, that irradiates the scene, the reflected light, it means the colors, will be different as well. That’s why white balance is so important in color photography. In monochrome or black and white it is not a mayor issue, specially in digital photography, because we can adjust the final image to match the tones of grays that we want.
How to use the white balance.
To understand the process, just imagine the light at dusk. Objects under that light get an orange tone. Our brain doesn’t try to render them with their real colors. The color of dusk light overcomes the rest, and all the image has that special orange-gold color. We can try to force that image to match as close as possible the real colors, but depending on the situation, this effort might be a waste of time.
Don’t confuse white balance as a way to render always the real color of things. Think about it as a way to render the image as real as the one we are seeing with our eyes.
These are the common symbols that you can find in any digital camera. They represent different kind of lights.
Usually it’s more comfortable to set the white balance in automatic (AWB), so in case of a hurry to shot, we don’t have to think about the light and set it manually. Just let the camera sensors decide for us. In case of low light environment, specially in closed locals with different kind of lights, the pictures tend to have a reddish color. To avoid this is not easy. It also depends on the camera.
Usually DSRL cameras and also some compact cameras, let you set the white balance based on the light temperature in Kelvin degrees. Just think that light can be expressed in temperature, the sun is the highest and the blue of a gas fire in the kitchen is one of the lowest. Based on this, setting the temperature as low as possible, will help to overcome that reddish light.
This is the menu to set the light temperature in a Nikon D200. The showed temperature, 2500K is the lowest and the highest is 10000K
Some cameras, like the Canon G11, have a superb automatic white balance based on the environment. This let you set the white balance in really hard situations with low light conditions.
Anyway, in case the white balance was not properly set, if you shot in RAW and you use a good edition software like Lightroom or Aperture, this can be easily fixed to match it as close as possible to the real colors.
Just remember. White balance has a direct relationship with the way colors are rendered in the picture. So before you shot in an environment with artificial light or if you are going to use a flash, think about the white balance.