The purpose of white balance adjustments are to compensate for the color cast of the "white light" which illuminates your subject. Human perception of white automatically adjusts for very subtle color casts of different "white light" sources. "White light" sources vary in their exact color slightly toward green-blue or yellow-red ends of the visible spectrum. Different kinds of light sources vary in the amounts of different colors they produce that combine to appear "white" to a human being. A modern digital camera makes an attempt to mimic the human perception adjustment when set for automatic white balance. This accounts for the unwanted color cast which a digital camera photo takes on when the camera's white balance is improperly set. Most digital cameras do have fixed and automatic white balance settings. While automatic white balance may not always produce the best results, some cameras do better than others.

The reality of dealing with different colors of "white light" sources is well known in photography circles and textbooks. Color temperature in degrees Kelvin is often used to describe the color of "white light". Previous to the wide acceptance of digital cameras, film photographers used colored filters and also the composition of film materials to make these adjustments. You may feel comfortable that you can produce excellent pictures without understanding the scientific details. In order to get great results, pay attention to the kind of light source that you are working with. If you can avoid mixing light sources it becomes very easy because they fall nicely into categories.

The best way to understand this first hand is to perform an easy experiment using your digital camera. Pick a scene illuminated with a single kind of "white light" source and be sure to include some "white" objects. Then, shoot the scene using each of your camera's fixed white balance settings.

The following fixed white balance settings are typical for a Nikon:

Fine -- for blue sky direct sunlight
Cloudy -- for overcast sky sunlight
Incandescent -- for ordinary tungsten filament light bulbs
Fluorescent -- for white neon gas tubes
Speedlight -- for strobe light flash

For your experiment, I suggest using the first four of those above. For example, illuminate your scene with Incandescent lamps and shoot with the Incandescent setting. Follow this by shooting using Fine, Cloudy, and Fluorescent. When you compare the shots side by side, you should notice a distinct color cast in the last 3 shots. Chances are good that the shot with the Incandescent (the correct) setting will be the best of the four.