Definition
A small electrical current that flows through a photoelectric device, such as a photocell or image sensor, even when no light is striking it. It is caused by the natural thermal activity of electrons inside the device and represents an unwanted background signal that must be accounted for when measuring or amplifying the device's true light-induced output.
Plain English
A tiny bit of electrical current that a light-sensing component produces on its own, in the dark, just because of heat inside it. It is not caused by light, but it shows up in the signal anyway and has to be allowed for.
Context Anchor
Seen in aircraft electronics and instrument discussions involving light-sensing circuits or optical sensors.
Derivation
From 'dark' (without light) and 'current' (a flow of electricity). The name describes the effect directly: a current that exists even in the dark. Knowing this makes the concept easy to remember -- it is the current you get when there should be none.
Why Pilots Care
Dark current can act like background noise in a light-sensing circuit, so avionics and instrument systems must account for it to avoid weak or false signals.
Analogy
Like the faint hiss you can hear from a stereo speaker even when no music is playing. The hiss is not the music, but it is always there in the background, and good equipment is designed to keep it small.
Grounding Statement
If a covered light sensor still produces a tiny electrical signal, that signal is dark current.
Intuition Check
Dark current is not current used for lighting at night. It is unwanted or background current that exists in a light sensor when no light is present.
Example Sentence 1
The infrared sensor's dark current rises with temperature, so the unit is cooled to keep its readings accurate.
Example Sentence 2
Excessive dark current in the night-vision system produced noise on the display.