What is the difference between normal headlamp and xenon headlamp?

Answer 1

A "normal" (halogen) headlamp uses a bulb that contains a coil of tungsten wire called a filament inside a small, thick glass or quartz capsule. The space within the capsule is filled with a mix of gases including some iodine or bromine compounds known generally as halogens. When the power is switched on, it flows through the tungsten wire, which heats up white-hot and that's your light source for the headlamp.

An HID (high-intensity discharge, "xenon") headlamp does not have a filament inside the capsule. Instead, it has a pair of electrodes separated by a gap (similar to a spark plug). The capsule is filled with Xenon gas and metal salts. When the power is switched on, it goes to an electrical ballast which steps up the vehicle's 14-volt line current to several thousand volts to jump the gap between the electrodes. This starts an arc, which heats up and vaporizes the metal salts, which then make the arc glow much brighter, and that's the light source for the headlamp.

Only headlamps designed and built as HID headlamps can safely and effectively use HID bulbs. Halogen headlamps must use halogen bulbs. "HID kits" are widely available, but they are (all) illegal and dangerous.

Some halogen bulbs are promoted using the word "xenon". All halogen bulbs contain xenon gas as an ingredient in the fill gas mix. To a certain extent, increasing the proportion of xenon permits the filament to burn brighter without shortening its lifespan. But "xenon" is also used (falsely) to promote bulbs that have blue glass instead of clear glass. These blue-glass bulbs imitate the color, but not the output or performance, of real HID headlamps.