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Retro-reflectors are characterized by the fact that an impinging light ray is reflected in parallel. The reflector does not need to be mounted at a right angle to the light ray. Vibrations and distortions in the wall where the reflector is mounted do not cause any disturbances either. Another advantage lies in the fact that possibly interfering light is also reflected in on itself and can thus not reach the receiver.
The retro-reflecting prism has the shape of an even pyramid, the lateral surfaces of which are made up from isosceles, right-angled triangles. Light rays coming in through the base surface are completely reflected by the lateral surfaces and are then scattered back through the base.
For distances of 20...100 m.