IEC 60357: Tungsten Halogen Lamps — How the Halogen Cycle Extends Filament Life in Quartz Envelopes

Halogen Lamps Last 2–3× Longer Than Incandescent — The “Halogen Cycle” Chemistry Miracle

IEC 60357:2002 specifies tungsten halogen lamp requirements. In standard incandescent lamps, tungsten evaporates from the filament and deposits on the bulb wall — the bulb blackens, the filament thins, and eventually fails. Halogen lamps add trace halogen (iodine or bromine) — evaporated tungsten reacts to form tungsten halide (WI₂/WBr₂), which decomposes near the hot filament (>1,400°C), redepositing tungsten back. This “halogen cycle” continuously recycles filament material.

TNLab — The halogen cycle is a classic case of chemistry meeting electrical engineering — a few ppm of halogen enables filament “self-repair.”