I guess that K is what this number represents, but the K scale is not totally relevant for white balancing.
The K number for a light source is a very rough representation of its "whiteness". In the real world, light sources have different spectral curves, and white balancing from a reference object respects this, multiplying the impression on each channel with the correct coefficient for the light to appear white. Daylight has a different spectral curve than most artificial light sources, and it is very different from the light sources for which the K scale is defined, black body radiation. In fact the only light sources that are true K radiators are incandescent lamps.
So LED bulbs, fluorescent lamps of any kind, or discharge lamps (including electronic flash), are not K radiators and do not really cling to the K scale for white balancing.
That is why we need a reference for white in the image as a starting point for white balancing. We need a reference, for setting our three channel coefficients closer to the desired values.
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There's a very informative posting by xpatUSA on the subject of auto white balancing, with links to relevant sources (very technical papers), which explain much of what has been said in this thread about white balance, and maybe to some degree can shed light on my rather rigid opinion on "AWB"
Three questions about white balance
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