Why is light used instead of x-rays in the sensor?

• A. Silicon is light-sensitive
• B. X-rays are dangerous
• C. Light is cheaper
• D. Sensor only detects light

Answer: (A)

Light is used because the sensor is made of silicon, a material that naturally responds to visible light by creating electron-hole pairs when photons are absorbed. Those charge carriers can be collected to produce an electrical signal directly proportional to the light intensity. X-rays interact with matter very differently and would not be efficiently detected by silicon in this direct way; detecting them would require a different detector design (often a high‑Z material or a scintillator to convert x-ray energy into visible light first), adding complexity and cost. So the fundamental reason is that silicon is light-sensitive and provides a direct, efficient photoresponse to visible light.