Definition
An incandescent lamp with a tungsten filament enclosed in a quartz envelope filled with iodine vapor. The iodine combines with tungsten that evaporates from the hot filament and redeposits it back onto the filament, which keeps the envelope clean and extends lamp life. Quartz is used instead of glass because it tolerates the high operating temperatures required for the iodine cycle to work.
Plain English
A very bright, long-lasting bulb that uses a quartz outer shell and iodine gas inside to keep the filament from wearing out as quickly as a normal bulb.
Context Anchor
Commonly encountered in aircraft landing lights, taxi lights, and other high-brightness aircraft lighting installations.
Derivation
Named for its two key parts: the quartz envelope (which can handle the heat) and the iodine gas inside (which recycles tungsten back onto the filament). The term describes the construction, not the light it produces.
Why Pilots Care
Delivers reliable high-intensity light for night operations and preflight inspections without rapid dimming.
Grounding Statement
Picture a small, very hot bulb behind a landing-light lens, built to stay bright without the glass turning dark inside.
Intuition Check
Do not read quartz-iodine as a lamp that burns quartz or iodine as fuel. The filament makes the light; the quartz handles the heat, and the iodine helps keep the bulb clear.
Example Sentence 1
The aircraft's landing light uses a quartz-iodine lamp for high brightness and long service life.
Example Sentence 2
During the preflight, the mechanic replaced a burned-out quartz-iodine lamp in the left landing light.