A light curtain for the optical detection of shading objects in an area to be monitored, wherein the area to be monitored is repeatedly swept over by a collimated light beam of variable direction. The power of the light crossing the area is measured, shadow boundaries, position and size of a shading object are deduced by an evaluating control from the temporal profile of the measured power with knowledge of the temporal profile of the direction of the light beam. An optical detector area embodied as a planar optical waveguide is arranged along the edge of the area to be monitored, photoluminescent particles being integrated into said optical detector area and one or more photoelectric sensors being fitted to the optical detector area. Using the light curtain, shading objects can be detected with very good resolution, the light curtain can be robust and can have a low production cost.