A light grid detects includes a number of light emitting transmitters. The transmitted light rays of the individual transmitters are imprinted with a code that characterizes the transmitted light rays. The transmitters are activated cyclically and successively. Corresponding receivers aligned with the transmitters form transmitter/receiver pairs. The receivers are activated continuously for reception of the transmitted light rays. An evaluation unit coupled to the receiver outputs generates an object detection signal in dependence on the signals received at the receiver outputs. The received signals are conducted in parallel to evaluation unit inputs. Only the received signals associated with the active transmitter are recorded and stored in the evaluation unit by muting the inputs onto which the signals received by the remaining receivers are conducted. The correctness of the codes transmitted by the transmitters and their sequence are checked in the evaluation unit by evaluating the stored received signals.