Definition
A semiconductor device that emits visible or infrared light when an electric current passes through it in the forward direction. The light is produced directly by the movement of electrons across a junction inside the device, with no heated filament involved.
Plain English
A small electronic part that gives off light when electricity flows through it. It does not have a glowing wire inside like an old-style bulb -- the light comes straight from the electronics.
Context Anchor
Seen in aircraft electrical systems, cockpit indicator lights, annunciator panels, displays, and lighting equipment descriptions.
Derivation
From 'diode' (a two-terminal electronic part that allows current to flow one way only) plus 'light-emitting' (gives off light). Knowing it is a diode explains why polarity matters: connect it backwards and it will not light up.
Why Pilots Care
LEDs provide reliable, low-power, long-life lighting for critical cockpit instruments and exterior lights, reducing electrical load and maintenance.
Intuition Check
Do not think of a light-emitting diode as just a tiny light bulb. A light bulb glows from a hot filament; a light-emitting diode makes light electronically and normally works only when current flows through it in the correct direction.
Example Sentence 1
The master caution panel uses LEDs, so the warning lights stay bright and reliable for thousands of flight hours.
Example Sentence 2
During the night flight, the wingtip navigation lights used LEDs that remained bright without overheating.