Which photocell configuration detects the target by receiving light reflected from the target back into the sensor?

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

Answer: (B)

Diffuse sensing relies on the target itself to reflect light back into the same sensor that emitted it. When the target is within the sensing field, the light that bounces off its surface returns to the sensor and is captured by the receiver, signaling presence. This setup doesn’t require a separate emitter/receiver pair or a dedicated reflector.

This is different from a transmitted beam arrangement, where the emitter and receiver are separated and the target is detected by interrupting the beam rather than by reflection back to the sensor. It’s also distinct from retro-reflective configurations, which depend on a reflector placed behind or around the target to bounce light back to the sensor, rather than relying on the target’s own surface reflection. Some sources call this type “reflective” sensing, but the specific idea described—light returning to the sensor from the target’s surface—fits diffuse sensing best.