Which photocell configuration uses a separate reflector to bounce light back to the receiver?

• A. Transmitted beam
• B. Diffuse sensing
• C. Reflective mode
• D. Retro-reflective

Answer: (D)

Retro-reflective sensing uses a dedicated reflector placed opposite the sensor. The emitter sends light toward that reflector, which bounces the light back to the receiver. When an object passes between the sensor and the reflector, the reflected beam is interrupted, and the sensor detects the change. This arrangement gives stable detection even with some misalignment or distance variation because the light has a fixed return path via the reflector. In contrast, through-beam uses separate transmitter and receiver with no reflector, diffuse sensing relies on light reflected off the object itself back to the receiver, and reflective mode uses the object’s reflection with no separate reflector involved.