Colour temperature is the scale that measures how 'warm' (yellow) or 'cool' (blue) light from a source is. It is measured using the Kelvin scale (abbreviated to 'K') and the higher the number the cooler the light is.
For example, a normal candle emits a warm yellow light of roughly 1000K, while a blue sky would measure around 9000K.
Our light sources range from 2000K to 3000K and we also have a number of Dim-to-warm products, where colour temperatures changes as the source is dimmed. Read more about Dim-to-warm here.