The spectrum of light is seen in a rainbow or from a prism, and it includes all of the visible colors. We tend to organize color into three primaries (red, green,and blue) and three secondaries (yellow, cyan, and magenta). When primaries of light are combined, the human eye sees white light

the intent of most light sources is to produce white light, of whose appearance there are two measures:

• Color temperature, which describes whether the light appears warm , neutral, or cool (bluish). The term temperature relates to the light emitted from a metal object heated to the point of incandescence. For instance, the color temperature of an incandescent lamp is about 2700K.
• Color rendering index (CRI), which describes the quality of the light on a scale of 0 (horrible) to 100 (perfect).