The principle of photoelectric sensor detection is that the beam of light emitted by the projector is blocked or partially reflected by an object. The photodetector makes judgments and reactions based on this.

When receiving light, the photoelectric sensor has an output, known as "bright pass". When the light is blocked or lowered by a certain value, the photoelectric sensor has an output, known as "dark pass". The intensity value of the photoelectric sensor's action is determined by many factors, including the target's reflection ability and the sensitivity of the photoelectric sensor. All photoelectric sensors use modulated light to effectively eliminate the influence of ambient light.