When a light wave passes through the scanning reticle, it is diffracted into three partial waves of the orders +1, 0, and –1, with approximately equal luminous intensity. The waves are diffracted by the scale such that most of the luminous intensity is found in the reflected diffraction orders +1 and –1. These partial waves meet again at the phase grating of the scanning reticle where they are diffracted again and interfere. This produces essentially three wave trains that leave the scanning reticle at different angles. Photovoltaic cells convert this alternating light intensity into electrical signals.