Which term describes the percentage of the detector element area devoted to the detection layer?

• A. Fill factor
• B. Pixel density
• C. Quantum efficiency
• D. Dynamic range

Answer: (A)

The concept being tested is the proportion of a pixel that is actively collecting signal. This is known as the fill factor—the percentage of the detector element area devoted to the detection layer. When a pixel has a high fill factor, most of its area is capable of sensing photons, which improves sensitivity and spatial sampling because more of the incoming light contributes to the signal rather than being lost to inactive gaps or supporting electronics. In contrast, pixel density refers to how many pixels fit in a given area (not how much of each pixel is active), quantum efficiency describes how effectively incoming photons are converted into a detectable signal, and dynamic range is about the span between the smallest and largest detectable signals.