A true HID bulb uses a ballast to ignite the chemical mixture inside. It does not use a filament.
- Xenon is 300 times brighter than halogen
- Xenon can last 10 times longer than halogen
- Xenon produces cleaner, whiter, brighter and safer light
- A 35W Xenon bulb consumes less power than a 55W Halogen bulb
- Halogen bulbs burn hotter than the same wattage Xenon bulbs
Halogen bulbs operate at 12V and use old lighting technology by heating a wire filament to emit light. Over a short period of time that wire filament becomes brittle, and small vibrations caused by everyday driving causes damage to the halogen filament affecting it’s light output and the bulb’s reliability.
Source : What’s the difference between HID and Halogen lights? | Better Automotive Lighting Blog