Which term describes how much light is blocked in a photoelectric detector?

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

Answer: (D)

When you’re talking about how much light is blocked in a photoelectric detector, the key idea is obscuration. Obscuration rate captures the fraction of the incoming light that cannot reach the sensor because part of the aperture or optical path is blocked by an obstruction or shading. This directly determines how much signal the detector can receive, since a higher obscuration means less light and a weaker signal, which can affect calibration and sensitivity.

Rate of diffusion isn’t about blocking light—it describes how particles or photons spread out over time. Rate of diffraction deals with light bending around edges and spreading into new directions, which changes the distribution of light but doesn’t quantify how much is blocked. Obfuscation rate isn’t a standard, meaningful term in this optical context. So obscuration rate is the correct term to describe how much light is blocked.