The light colour is indicated in Kelvin (K). Kelvin basically defines a temperature. This stands for the temperature an object should have (glowing coal, for example), so that its light creates the same colour impression as the light source: 1 °C = 274 K | 2700 °C = 2973 K. The colour temperature indicates how warm or cold white light in particular is. The lower the Kelvin value, the warmer the light. The light of a commercial light bulb would correspond here to approx. 2700 K. The higher the Kelvin value, the colder, so the light becomes bluer. Daylight is set at around 7000 K in comparison.