In a photoelectric smoke detector, what term describes how much light is being blocked?

• A. Obscuration rate
• B. Rate of diffusion
• C. Rate of diffraction
• D. Rate of obfuscation

Answer: (A)

In a photoelectric smoke detector, the important idea is how much of the light beam is blocked by smoke inside the optical chamber. That blocking is called obscuration—the fraction or amount of light that cannot reach the sensor. When we talk about how quickly this blocking changes as smoke enters or accumulates, we use obscuration rate to describe that dynamic. So the term describing how much light is being blocked is obscuration, and phrasing it as obscuration rate conveys the rate at which the beam is being obstructed. The other terms refer to different light behaviors (diffusion and diffraction) or aren’t standard terminology for this context, so they don’t fit as well.