color temperature - technical definition

The measurement of color expressed in Kelvin (K). The reason this measurement is called a "temperature" is because it was derived from a theoretical object called a "black body radiator." When the radiator is heated, it changes from black to red to yellow to white to blue. The lower the Kelvin rating, the "warmer" or more yellow the light. The higher the rating, the "cooler" or more blue the light. See white balance.

                        Approximate
                        Temperature
   Lighting             In Kelvin

   Candle               1,800 K
   Indoor tungsten      3,000 K
   Indoor fluorescent   4,000 K
   Outdoor sunlight     5,500 K
   Outdoor shade        7,500 K
   North sky           28,000 K