Which sensing category uses a dark-operate output when no target is present?

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

Answer: (D)

Diffuse sensing relies on light reflected directly from the target. Without a target, there is no reflected light reaching the receiver, so the idle state is darkness. If the sensor is wired for dark operate, the absence of light turns the output ON, meaning you get a signal when no target is present. Other sensing categories depend on a continuous light path: through-beam (opposed) and transmitted beam provide light to the receiver even when no object is in the path, and retro-reflective relies on a reflector to return light, so their idle state isn’t dark by default. This makes diffuse the category that uses a dark-operate output in the no-target condition.