Xenon, also know as hid is a lighting technology which has been around in passenger since the mid 1990s. It is provides a significant light increase over halogen passed lamps. Xenon lamps are designed to last for around 2000 hours!! NO, if one of your headlights is out, you cannot just plug a halogen bulb into a xenon based housing, the bulbs have differnt sockets. And if you already have xenon headlamps you would not want to go back to halogen, because you would definently regret it. Check ebay for a used housing.