Definition
A two-terminal semiconductor device that conducts electric current when light strikes its sensitive surface. The amount of current produced is proportional to the intensity of the light, allowing the photodiode to act as a light sensor.
Plain English
A small electronic part that lets electricity flow through it when light hits it. The brighter the light, the more current it passes, so it can be used to detect or measure light.
Context Anchor
Seen in aircraft electrical and electronic system descriptions, especially where a system senses light, flame, position, or a reflected beam.
Derivation
From Greek 'photo' meaning light, and 'diode' meaning a device that allows current to flow in one direction. Together: a one-way electrical device controlled by light.
Why Pilots Care
Photodiodes are the working element behind several warning and detection systems in modern aircraft. Knowing they respond to light helps a pilot understand why some sensors can be fooled or blocked by dirt, ice, or unusual lighting conditions.
Analogy
A photodiode is like a tiny automatic switch that reacts to light instead of being pushed by a finger.
Intuition Check
A photodiode is not the same as a light bulb or a light-emitting diode. It mainly senses light; it does not mainly make light.
Example Sentence 1
The fire-detection loop uses a photodiode to sense the light from a flame inside the engine compartment.
Example Sentence 2
During the preflight check the technician verified that the photodiode produced the expected current when a light source was applied.