A charge-coupled device (CCD) does all of the following except:

• A. Convert light into X-ray photons
• B. Convert light into electrical charge
• C. Store charge in capacitors
• D. Detect light via photosensitive material

Answer: (A)

The main idea is that a CCD detects light by converting photons into electrical charge, not into photons of a different type. When light hits the photosensitive silicon, photons impart enough energy to release electrons, creating electron–hole pairs. Those charges are collected in each pixel’s potential well, effectively storing the charge in tiny capacitors. The stored charge then moves through the device to a readout circuit, which translates the amount of charge in each pixel into a digital image. This is why the sensor is described as converting light into electrical charge, and why it stores that charge in capacitors and detects light via the photosensitive material.

What isn’t part of the CCD’s operation is turning light into X-ray photons. A CCD does not generate photons; it detects and records the light by producing and storing electrical charge. (Some sensors can detect X-rays by absorbing them and producing charge, but the fundamental action is still charge generation from incident photons, not creating X-ray photons.)