Colour temperature

Colour-temperature-chromaticity-diagram A specification of the colour appearance of a light source, relating the colour to a reference source (Planckian radiator) heated to a particular temperature, measured in Kelvin.

The CIE chromaticity diagram shows the evolution of this Plankian radiator (also called a black body radiator) through the different colours of the diagram.
For instance, a light source that has a colour temperature of 6000K emits a cool white light, as shown on the diagram for the black body heated at 6000°K.