spectrophotometer :
In contrast to a densitometer which measures the reflection of a colour in order to analyse the thickness of a colour layer, a spectrophotometer can measure throughout the entire spectrum of visible light by illuminating the measured area. The complete area is made visible from infrared to ultraviolet. These meters can better evaluate the remission values and possible colour deviations between two points can be calculated. A certain range of spectral colours is detected and processed by the sensor of a photocell .