CRI stands for Color Rendering Index and describes in numbers to what extent artificial light is similar to natural light. In color theory, white is the maximum range of red, green and blue. In nature, perfect white is achieved when sunlight falls vertically on the earth at noon, that is, no wave areas are broken off into the atmosphere. In this case we speak of a CRI of 100. Reflections, on the other hand, take place in the evening and in the morning; the sky turns red, which means that the blue components of the light are broken off by the atmosphere.

With book scanners, developers try to get as close as possible to the value 100 for the light source, usually a CRI of 80-95 is achieved. However, this value is not solely responsible for the quality of the light; valid statements can only be made in connection with the color temperature. The values can also fluctuate depending on the current operating temperature of the light source.