Abstract: An arrangement for controlling a constant signal amplitude in an opto-electronic scanning system, for example in an incremental angle indicator, utilizes diaphragms which are periodically interposed between a light source and a light receiver. The brightness of the light source can be regulated by a light receiver which detects brightness. When arranged opposite a diaphragm gap, the light receiver of the opto-electronic scanning system supplies at the received value of the light to a storage device which stores the value for the duration of a dark phase produced by the diaphragm and the light value is applied to a circuit for regulating the brightness of the light source.