HID

A high-intensity discharge lamp produces light by striking an electrical arc across two electrodes inside a sealed bulb filled with xenon gas and metal halide salts. The arc temperature reaches around 4000 kelvin, generating a bright white or bluish light roughly 2.5 to 3 times brighter than a comparable halogen bulb while drawing similar electrical power. This efficiency gain made HIDs attractive for vehicle headlights starting in the late 1990s, where they became standard on many premium and luxury models.

HID headlights require three additional components that halogen systems do not: a ballast unit that converts the vehicle's 12 or 14 volt DC supply into the 20,000+ volt pulse needed to strike the arc, an igniter module that provides that initial spike, and a shutter or leveling mechanism to aim the beam since HID brightness can dazzle oncoming drivers if the headlight tilts upward. Without these controls, an HID installation creates a hazard.

The light color from HID lamps varies by the halide mixture in the arc tube. Bulbs rated at 4300 kelvin appear yellowish-white and offer better visibility in fog; 5000 to 6000 kelvin bulbs look pure white and are common in mainstream applications; 8000 kelvin and higher produce blue-tinted light favored for appearance rather than function. Lifespan typically runs 2000 to 3000 hours, significantly longer than halogen but finite. The arc must stabilize for several seconds after ignition, so HID headlights cannot flicker on and off rapidly.

HID technology declined in new vehicle designs after 2010 as LED headlights matured and offered comparable or superior brightness with instant-on capability, lower heat output, and longer operating life. However, HID remains common in older vehicles and persists in some truck and commercial applications. Aftermarket HID conversion kits for halogen-equipped vehicles are sold widely but often operate without proper ballast integration, creating unreliable lighting and glare that puts other drivers at risk.