Xenon/Halogen Incandescent Lamps
Identical non-SureFire miniature lamps. Left lamp is unused, right lamp shows tungsten deposits after several hours of use. Incandescent lamps produce light by using electricity to heat a small coiled tungsten metal wire, which is enclosed within a glass bulb filled with special gases, to a high temperature — around 2,500 to 3,000 degrees Celsius — at which point the wire glows white-hot. The miniature incandescent lamps that SureFire uses in its WeaponLights and flashlights are not typical off-the-shelf products. They are state-of-the-art devices with the following features:
Custom Filaments — The incandescent lamps (light bulbs) used in our WeaponLights and flashlights are designed around a specific power supply, light output, and runtime. Filament performance varies according to wire diameter, filament length, filament coil diameter, total coils, and coil-to-coil proximity. Finally, the finished filament must withstand the vibration and G-forces produced by firearms.
SureFire MN21 lamp, showing heavy duty high-output filament. Xenon Gas — The high temperature of the lamp filament causes tungsten atoms to boil off and migrate to the cooler glass wall of a lamp, where they condense to form a dark light-blocking layer. Adding a high-pressure inert gas inhibits tungsten boil-off, which reduces the rate of tungsten atom deposition and lengthens the operating life of the lamp. The gas also permits increased filament operating temperature, which in turn increases light output for a given power consumption rate. Argon and krypton are often used as the inert fill gases, but they don't work as well as xenon. Although xenon is much more expensive, SureFire uses it exclusively to provide optimum lamp performance.
Halogens — To maximize their operating life and light output, some SureFire lamps contain a proprietary mix of halogens, a family of elements that includes fluorine, chlorine, bromine, and iodine. Inside a functioning incandescent lamp, tungsten atoms boil off the filament, migrate toward the cooler areas near the lamp wall, and combine with halogen atoms to form a tungsten halide vapor. This vapor migrates back to the lamp filament, where high temperature breaks it down again into tungsten and halogen atoms. The tungsten atoms are re-deposited on the filament and the oxygen and halogen migrate back toward the bulb wall to re-combine with new boiled-off tungsten atoms. This continuous process, called the halogen cycle, keeps the lamp's glass walls comparatively clean of light-blocking tungsten deposits.
Incandescent lamps produce a broad spectrum of light (including infrared) and can be made to have a high maximum lumen output, but they are comparatively inefficient users of power, and their lumen output level is effectively non-adjustable.