How long do they last? I have always been of the opinion that driving with my lights on the minute things start to go overcast/dim makes sense. Volvo make all their cars do it as standard and I can see the reasoning behind it. It also makes my car stand out that little bit more (only being race blue & all...! ).

My concern is how long the bulbs last for. Not fussed about the rears as they are dead easy & cheap to replace (Ben @ Shark performance changed one of them that failed en route free of charge whilst we were chatting). The car is 56 plated and I have my lights on the ay to work & on the way home from the gym so they get used a fair amount of time.

The life of xenon's varies.

Xenon's are designed to last a lot longer than normal tungsten bulbs, approximately 10 times as long.

Filament headlight bulbs are generally good for around 300 hours so you should look to get 3000+ hours from your xenon's

The difference with xenons is that there are other components too such as the ignitors and balasts to considor.

The thing that does drastically shorten the life of xenon's is repeated on/off cycles.

The price of a replacement bulb varies from £30 (eBay) to around £80 (genuine) so I wouldn't worry!

You're doing the right thing. The amount of morons I see driving around in poor conditions/at night with side lights or even no lights at all beggars belief. These are probably the people who are then surprised that people pull out in front of them or cut them up. I pulled out in front of someone a couple of years back who I completely didn't see, as he had side lights on and the guy behind him had his lights on, making him totally invisible. Other than stupidity I don't know why they do it, maybe to save money on bulbs?! An insurance excess is a lot more! Keep the lights on and don't worry about it, they wear out when they wear out.

As has been stated, HID lamps do typically last many times longer than halogen bulbs. Unfortunately it seems that the ballasts also fail from time to time - so its not just lamp replacement that must be considered. Ballasts (a kind of ECU which enegerises the lamps) generally cost a lot more than the lamps. Each lamp has its own ballast mounted at the rear of the headlamp.

One thing to be aware of is that HID lamps do tend to deteriorate over time - their output declines. At some point (after a few years) you may therefore wish to replace the lamps to restore full output.