A detector surface which is based on optical signals and arranged as a flexible enveloping surface around the body in order to detect whether and where the illuminated indicator strikes the body. The detector surface composed of one or more planar optical fibers, wherein at least one layer of a planar optical fiber has photoluminescent properties, and wherein photodetectors are arranged on the planar optical fiber such that they can decouple light from the optical fiber and detect it. The planar optical fiber is designed as a film made of a transparent polymer having a thickness of 30 to 500 μm and the photodetector is arranged at a distance from all edges of the optical fiber on the optical fiber.