Color Temperature

Lighting is measured in Kelvin (color temperature)
Day light is approx - 6500 Degrees Kelvin
Indoor Lighting is approx - 3200 Degrees Kelvin

Here is a brief description I found on Wiki -

The kelvin is often used in the measure of the colour temperature of light sources. Colour temperature is based upon the principle that a black body radiator emits light whose colour depends on the temperature of the radiator. Black bodies with temperatures below about 4000 K appear reddish whereas those above about 7500 K appear bluish. Colour temperature is important in the fields of image projection and photography where a colour temperature of approximately 5600 K is required to match "daylight" film emulsions.