Definition
A gas-filled electron tube in which current flow through a low-pressure gas produces a steady, soft glow. The voltage drop across the tube remains nearly constant over a wide range of current, which makes it useful as a voltage regulator or voltage reference in electrical and electronic circuits.
Plain English
A small sealed tube containing gas that lights up when electricity passes through it. Because the voltage across it stays steady even as the current changes, it can be used to hold a circuit's voltage at a fixed value.
Context Anchor
Seen in aircraft electrical systems, older radio equipment, instrument lighting, and maintenance descriptions of electrical components.
Derivation
Glow describes the soft light the gas emits when ionized. Discharge comes from the Latin dis- (apart) and carricare (to load), meaning to release or let out — here, the release of electrical energy through the gas. So the name simply describes what the device does: it discharges electricity through gas, and glows while doing it.
Why Pilots Care
Pilots don't operate these directly, but understanding that older avionics rely on gas-filled regulator tubes helps when reading maintenance documentation or troubleshooting legacy equipment.
Analogy
A small neon indicator lamp is a familiar example of the same basic idea: electricity passes through gas in a sealed tube, and the gas lights up.
Intuition Check
Do not read “discharge” as spilling, draining, or emptying. In this term, it means electricity flowing through gas inside the tube.
Example Sentence 1
The radio's power supply used a glow-discharge tube to keep the reference voltage steady.
Example Sentence 2
Older aircraft radios sometimes used a glow-discharge tube as a simple visual indicator of power presence.