A light barrier having a signal path (1) between a first transceiver arrangement (2), emitting a signal beam (4), and a mirror, returning the incident signal beam (4), allows reliable operation even when the length is great and under changing ambient conditions by virtue of the mirror being in the form of a second transceiver arrangement (3) and by virtue of both transceiver arrangements (2, 3) having a receiver (6), a controllable and encodable transmitter (8) and an evaluation and control device (7), connected to the receiver (6), for evaluating the intensity and an encoding of the received signal beam (4, 5), and for controlling the intensity and encoding of the emitted signal beam (4, 5), wherein the encoding is performed using a piece of information about the intensity of the received signal beam (4, 5).
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