HID Lamps

HID lamps do not use a tungsten filament, but instead use a clear quartz capsule (an "arc tube") fitted with electrodes at either end and containing high-pressure xenon gas and additional chemical components. When sufficient voltage is applied to the electrodes the gas inside the tube is heated and ionized, enabling it to conduct electricity in the form of an "arc" (basically a sustained electrical spark), and causing it to emit light. When functioning, pressure inside the arc tube rises to above atmospheric pressure.

HID lamps are extremely bright and extremely efficient and, with equal power input, they produce more than twice the lumens of an incandescent lamp with a longer operating life than comparable incandescent lamps. Since they have no filament to break or burn out, they are extremely resistant to shock and vibration. However, they are comparatively large, require a substantial power source, and their lumen output level is effectively non-adjustable.