Represent in absolute temperature K, that is, heating a standard black body when it is heated up to a certain degree where the color starts to change from dark red, light red, orange, white, blue, changed gradually and the color of the light source is the same as blackbody. We call the absolute temperature of the black body at that time the color temperature of the light source. Examples are as follows: Light source Color temperature Northern clear Sky 8000-8500k Cloudy sky 6500-7500k Summer noon sun 5500k Metal halide lamp 4000-4600k Afternoon daylight 4000k Cool camping lamp 4000-5000k High ressure mercury lamp 3450-3750k Warm camping lamp 2500-500k 3000k halogen lamp 3000k.