Definition
A fine wire, usually made of tungsten, inside a vacuum tube or incandescent bulb that glows and emits electrons or light when an electric current heats it to a high temperature.
Plain English
A thin wire inside a bulb or tube that gets hot enough to glow when electricity flows through it.
Context Anchor
Seen in aircraft lighting and electrical troubleshooting, especially when discussing bulbs for position lights, landing lights, or instrument lights.
Derivation
From the Latin filum, meaning 'thread.' The word describes the thread-like shape of the heated wire.
Why Pilots Care
A broken filament prevents the light from working, which can affect night visibility or required signaling.
Analogy
A filament is like the glowing wire in an old-style household light bulb: electricity heats the wire until it shines.
Intuition Check
Do not read filament here as just any thin thread or fiber. In aircraft electrical use, it usually means the tiny wire inside a lamp that produces light.
Example Sentence 1
The landing light was inoperative because the filament had burned out.
Example Sentence 2
Before the night flight the mechanic confirmed both position light filaments were intact.