Andrew Rodney , Apr 28, 2005; 11:31 a.m.
Color Temperature is a number (in Kelvin) that describes the color of light emitted by what is called a blackbody radiator. This is a theoretical object (the closest item in the real world that behaves as a blackbody is our sun).
It's somewhat dangerous to use color temperature to define what you want because the reality is if all light sources were true blackbodies a particular color temperature would produce the same color of light. Because natural materials are not theoretical blackbodies, heating them to a specific temperature creates deviates from the theoretical color from magenta to green. It's really much safer to use the term correlated color temperature (CCT) because many colors of white may correlate to the same blackbody color temperature. Different illuminants can have the same correlated color temperature.
This is one reason why the CIE defined the Standard Illuminants.These illuminants are defined spectrally meaning a certain amount of energy at each wavelength across the spectrum. This is an exact and non ambiguous description of color. D65 is an exact color, it is not a range of colors. If you have a color meter that reports color temperature of a light source many light sources that appear different could read the same, that's kind of a problem!
Rather than say 6500K, it's much safer to say a CCT of 6500K. The color you get from a 6500K light source can vary due to the shift of magenta/green. D65 is an exact, non ambiguous color that we can fingerprint exactly by viewing it's Spectral Power Distribution (SPD).
CCT and Blackbody curve