Just recently, an overheard conservation of a customer in a big box store went something like this: “I need this color temperature for my ceiling fan lights.” Certainly, retailers and manufacturers emphasize terms such as “color temperature” on their packaging. A quick look at retail store displays discloses that a color temperature range of 2700 to 3000 Kelvin (K) provides warm light (ideal for libraries or dining rooms). color temperatures of 3100K to 4100K yield a cool, neutral light (ideal for lobbies, retail stores, offices, and classrooms). Color temperatures of 4600K to 6500K produce a more intense blue-white light (ideal for hospitals and commercial use).
Why use the Kelvin temperature scale? Named after Lord Kelvin, the Kelvin scale measures absolute temperature. Absolute zero on the Kelvin scale refers to minimal movement of molecular energy or -459.7 degrees Fahrenheit. 373.16K equals 212 degrees Fahrenheit or the boiling point of water. Heating an object to 1000K causes the object to glow at low intensity in the visible spectrum. Increasing the Kelvin temperature continues to move the radiated energy into the visible spectrum.
The Kelvin Color Temperature scale works from the perspective of the heating of an abstract reference point called a “black body radiator.” As the temperature of the black body increases, it absorbs and then radiates all the energy. Incandescence refers to the emission of light by an object heated until it glows or radiates light. As the temperature of the black body radiator increases, the object begins to glow. Increasing the heating of the object causes the glowing color to shift from deep reds to oranges and then to yellows and ultimately to white. The characteristics seen with this shift refer to incandescent radiators that radiate light energy at all wavelengths of their spectrum. Incandescent radiators define color temperature.
The color temperature scale provides a convenient method for measuring the color of light radiated by an object using the temperature of the object of a reference. In addition, the use of color temperature places this measurement in human terms. For example, 1,930K on the color temperature scale refers to the measurement of light emitted by a candle flame while direct sunlight has a color temperature of 5,400K.