The color temperature of light describes the warmth or coolness of a particular light source. To best illustrate this, imagine a piece of metal being heated. The metal will initially turn red and as the heat increases the color will begin to turn yellow and then white, bluish-white and finally into deeper shades of blue. The temperature of the metal in this example is measured in degrees Kelvin. While lamps (light bubs) react differently to a heat source than metal, the same color temperature (Kelvins) are used to describe the light emitted by the source. It is important to note that this chart strictly indicates the color of light emitted and is not an indicator of the physical heat produced by the lamp.
In general, the warm colors are in the red-yellow area of the chart. On the other end, the cooler colors are in the blue area of the chart. Any easy way to remember this difference is the warm colors are those found in a flame while the cool colors are those often present on an overcast day. The opposite is true when discussing the Kelvin temperature of the various colors. Cool colors have a range of 3600-5500 K, while warm colors fall into the 2700-3000 K range.
Finally, different temperatures are best for different applications. Cool lights are generally preferred for visual tasks as they generate higher contrast. Warm lights are preferred for living spaces because they compliment skin tones and clothing better. For most indoor general and tasks applications it is recommended that you use strive to use a color in the 2700-3600 K range.