Aftermarket xenon conversion kits are illegal unless they are fitted with a complex self-levelling system. All manufacturer-fitted xenon lights have this feature as standard. 'Xenon' upgrade bulbs are not really xenon at all - they are conventional halogen bulbs that emit a whiter light to mimic the effect of genuine xenon headlights. Not sure if fitting the latter would cause your car to fail an MoT though, providing of course they were correctly aligned etc.

My experience of pukka xenon discharge (as opposed to xenon filled incandescent) bulbs was that they're very penetrative - with the dipped beam providing a non-fading arc up to the headlight range. That is, they seem to illuminate the 70-odd metres in front uniformly, whereas halogen type headlights get fuzzy & fady at range. I had a Skoda Superb with xenons & they were so good, i actually looked forward to the dark winter evenings!

I think the lenses & reflector bowls are also better in factory spec xenons - better quality components used. With the after-market high-output & xenon filled bulbs I think it very much depends on the quality & original performance of the lenses & reflectors, as my experience has been mixed.

On a Mercedes C-class I owned I fitted high-output incandescent bulbs & they made a real positive difference, but my current 2010 Mondeo doesn't seem to that much better with these than the standard bulbs.

So, if you're buying a car with factory fitted (proper) xenons, they'll probably be very good - if you're just upgrading bulbs, it will vary by car more.

Edited by woodbines on 21/11/2010 at 11:10

They make a world of difference on our S-max compared with my non-xenon equipped leon, especially on unlit roads. They are better in both dip and full beam, but especially fantastic on full beam. Of course you may never use this if you dont drive down quiet unlit roads. There are two types of factory fit Xenons as well - some cars have Xenon only for the dipped beam, ours (I believe) has them for the dipped and full beam. The S-max also has cornering lights which again make a difference only really on unlit roads

They were part of a package with the S-max. I certaintly wouldn't have spent an extra £700 or so to get them on the Leon, but would look out for them if buyijng a second hand car.

If you were to read I said they were non user adjustable which is correct,the fact you can turn screws that in turn adjust the lights are classed as non user not user. Is there a left right adjustment NO is there a dashboard leveler NO.

Edited by Andy Bairsto on 22/11/2010 at 18:07

Again you do not read what I have said,did I say there was a left right adjuster in the cabin NO. You could adjust them with a sledge hammer if you wanted I repeat there are no user adjustment for Xenon´ s.