Kelvin

Kelvin is the unit for the colour temperature, which specifies the colour of the light. The higher the value, the "colder" the effect of the light. Under 3,300 K the light is designated as warm white, between 3,300 K and 5,300 K neutral white and from 5,300 K cool white light is emitted.

See also:

Warm White
Neutral-white
Cold White