Contrast sensors are based on the intensity discrimination principle and detect even the smallest contrast differences between a mark and the background. The main area of application is the detection of print marks in printing, labeling and packaging processes. For sensors with RGB light, the sensor automatically selects the ideal emitting color red, green or blue for the respective contrast. As a result, even the slightest differences in contrast can be reliably detected. Sensors with white light have a very small light spot for the detection of color marks. Laser sensors can detect even the smallest print marks.