Abstract: A device for photoelectrically starting and stopping the operation of a bunsen burner in response to the shadow of an operator's hand holding an object to be heated includes a solenoid valve in a line supplying gas to the burner and electronic control circuitry having secondary and primary photoelectric cells arranged in a differential response circuit. Changes in the intensity of the ambient light are cancelled by the differential response circuit, while a hand shadow, which affects only the primary cell, triggers the solenoid valve, via a gate circuit and solenoid switch.

Abstract: A device for electrically starting and stopping the operation of a gas burner in response to the shadow of the user's hand holding an object to be heated, the device including a solenoid valve in the gas line and a dimmer circuit with a directional photoelectric sensor, a switching amplifier, and a valve relay controlling the solenoid valve. The dimmer circuit can be bypassed for continuous operation by means of a selector switch.