The invention relates to an optical sensor for motor vehicles, for detecting ambient parameters that affect vision, having at least one transmitter and at least one receiver for electromagnetic waves (light waves), in which a windshield is disposed in a measurement segment between the at least one transmitter and the at least one receiver and influences a wave propagation between the at least one transmitter and the at least one receiver in such a way that when a film develops on the windshield, and especially when wetting occurs from precipitation, an output signal generated by the receiver varies and serves to trigger a windshield wiper system. It is provided that at least one of the receivers (16, 20, 22) of the optical sensor (4) receives electromagnetic waves (light waves) of an ambient brightness of the motor vehicle and serves to trigger a light system of the motor vehicle.