The element in the imaging chain that converts light into an electrical signal is the:

• A. Diode
• B. Photodiode
• C. Capacitor
• D. Resistor

Answer: (B)

Light-to-electrical conversion in an imaging sensor is performed by a photodetector that responds specifically to light. A photodiode is a semiconductor device that generates current when photons are absorbed, creating electron-hole pairs. Under reverse bias, the photodiode’s current is proportional to the light intensity, so the signal you read out from each pixel reflects how much light hit that spot during exposure. In imaging sensors (like CCD/CMOS), the photodiode collects charge during exposure, and this charge is later converted to a voltage for processing.

A generic diode isn’t necessarily light-sensitive in a useful way for imaging; a capacitor merely stores charge, and a resistor mainly limits or dissipates current. So the device best suited to turning light into an electrical signal in imaging hardware is the photodiode.