Instead of a filament inside a bulb, the high-intensity discharge (HID) headlights make of electric arc to produce better luminosity. Metallic salts are ignited and vaporized inside the arc chamber to produce light. Technically known as gas-discharge burners, BMW E46 HID require the process of ignition in order to burn xenon or argon. These headlamps are said to give a more powerful light than the tungsten-halogen lamps for the same energy consumption.
Xenon gas is preferred as power source of HID headlamps because it provides sufficient lighting upon start up. On the other hand, argon gas, which is often used in streetlamps, requires some time to get to complete discharge of light. The distinguishing characteristic of BMW E46 HID is the bluish illumination produced when in use. They were first commercialized in 1991 as an aftermarket part for BMW 7 Series.
Most BMW E46 HID use alternating current (AC) ballasts in controlling the high-intensity electric discharges. Its operation begins with ignition wherein a spark is produced to burn the xenon. The current travels in a conducting tunnel, through which the high voltage is controlled. Upon reaching the arc chamber, this power, then, vaporizes the metallic salts. When vaporization is complete, luminosity is achieved and the ballasts continuous to produce more power so that the arc remains stable.