What does a Kelvin Rating mean? The Kelvin color temperature of the light source is the color of light emitted by a "black body" when heated to a certain temperature measured in Kelvins (K). As the heat of the material increases it undergoes a color change from the warm colors to cooler colors.
Unfortunately, the ratings when applied to a particular bulb mean almost nothing. When you see a bulb described as a 10,000K bulb, you can derive very little from that label. Some bulbs, depending on the manufacturer, have a yellowish color while others are bluer than the bulbs labeled as 20,000K. The Kelvin scale is now a marketing tool more than an unbiased indicator of bulb color. There are even bulbs out now that are marked 50,000K which is interesting, considering the visible part of the scale doesn't go that high.