Colour Temperature

In scientific terms, colour temperature is used to quantify and describe the colour of light emitted from a light source. Strictly speaking, it is the temperature in degrees Kelvin of a heated "black body radiator". When a piece of metal is heated it emits light progressively from a dull red through orange and yellow to bright white, so dull red has a lower colour temperature than yellow and white. When applied to light sources, the colour temperature accurately describes the light being emitted. For example, a candle flame has a colour temperature of 1,850 degrees Kelvin ( K ), a tungsten filming light is 3,200 deg K, and an HMI Daylight lamp is 5,600 deg K. Natural daylight can range from 2,000 deg K at sunrise / sunset through to 10,000 deg K for an overcast sky. 

In film & television terms, any imaging sensor (film or ccd) is sensitive to colour temperature. For example, a sensor balanced to reproduce correct tones at a daylight colour temperature of 5,600 K will not reproduce correct tones in tungsten light with a colour temperature of 3,200 K. Instead, the image will have an overall "orange" cast to it. This can be corrected either in camera by white balancing or using a colour filter, or at post production by "grading".