Retroreflective Photoelectric Sensor is used in a configuration where the sensor and the prism face each other. When no object passes through, the light emitted from the light-emitting surface passes through the prism and is received by the medium on the light-receiving surface, and is output as a collector current.

On the contrary, when an object passes between the sensor and the prism, the light is blocked by the object and the collector cannot be energized.

In addition, using prism mirrors has the advantage of single-sided wiring.