Now it's getting to winter people start to realise how poor their lights are compared to the latest generation of cars. A popular upgrade is to fit xenon headlight bulbs which give a 'whiter' light. I am not talking about the blue bulbs that seem popular with the boy racers (see below), genuine xenon bulbs will improve the light output as well as appearance (to some extent) of your headlamps. Please note: No bulbs that I have come across will give the same appearance as HID (high intensity discharge) lamps as fitted to high end cars like mercedes,bmw and audi's - this is down to the construction of the headlight and bulb itself - if you buy bulbs expecting the same effect you will be disappointed! -
New MOT regulations coming into force in 2012 will check for the correct operation of the headlight washers and self-levelling system if you have HIDs fitted - if you don't have these, your car will fail it's MOT.
See the section on lights at: http://www.direct.gov.uk/en/Motoring/OwningAVehicle/Mot/DG_4022109
Bulb upgrades are not illegal (as long as you fit the correct wattage), HID kits are. See http://www.dft.gov.uk/pgr/roadsafety/drs/hidheadlamps for further info.
"In summary it is not permitted to convert an existing halogen headlamp unit for use with HID bulbs. The entire headlamp unit must be replaced with one designed and approved for use with HID bulbs and it must be installed in accordance with the rules stated above."
The Technical Bit:
The bulbs will have a colour temperature rating (xxxx K), and is a measure of the 'whiteness' of the light emitted - it has nothing to do with the operating temperature of the bulb (ie how hot to the touch the bulb is). The lower the xxxx number is (say 3300K) the 'yellower' the light is, the higher the number (say 6000K) the 'bluer' the light will be, but the trade off is that the light output will appear to be less due to blue light being difficult to see by. Also because our eyes are more sensitive to the yellow end of the spectrum, a 50W blue bulb will appear dimmer than a 50W yellow bulb due to our eyes sensitivity. In wet conditions the water actually absorbs a lot of the blue light so the light output will appear even lower.
Note: The colour temperature of natural daylight at noon is between 5000-5500K.
So blue bulbs may look cool, but if you want to see where you are going and others to see you, avoid them like the plague!
The Non-Technical Bit:
So what am I using? Well I was running 90/100W standard halogen H4 bulbs (standard headlights should be 55/60W! ;-) ) but decided to change for Philips Vision Plus bulbs which seem to give the same amount of light output but with a better spread of light and a better colour (ie much 'whiter'); in our other car I have Ring Ultra Xenon bulbs which I am very impressed with (and would probably replace the Philips ones with when they go) despite the Philips bulbs getting a better review. I have also got a pair of Osram Silverstar bulbs for my fathers car as they got the best award for H7 bulbs in one of the motoring magazines, but haven't had an feedback from him as yet.
Update: 6/11/07: There is a new bulb on the market, the Osram Night Breaker which is (according to the manufacturers) supposed to give 90% more light output and be 10% whiter (I assume measured against standard halogen headlights). I will be trying these when I next require replacement bulbs but they are not cheap (at the moment) with prices at approx £20 for a pair of bulbs.
Update 1/10/08: The Ultra Xenons never failed before I got rid of my car so I never got to try the Nightbreakers so I can't comment on there performance and bulb technology has now moved on again. The latest bulb to get rave reviews is the Philips X-treme Power and I have a pair of these waiting to be fitted to my new car when it arrives, if they are better than the Vision Plus bulbs I will be impressed. Also just arrived on the scene are the Ring Xenon Max bulbs (so new they have not appeared in any reviews as yet!) and if they are anything like the Ultra Xenons by Ring, they should be excellent. I will probably try the X-treme Power bulbs in the dipped beam and the Xenon Max bulbs in the main beam.
Update 13/09/10: When one of the Philips X-treme Power bulbs (and yes, they were better than the Vision Plus bulbs) died recently I fitted Ring Xenon Max bulbs in the dipped beam as well and to be honest I was a little disappointed - the beam pattern from one of the headlights now seems to be poor (something to check when fitting new bulbs is to make sure they are located correctly in their holders) - not so poor as to warrant changing them but definitely not as good as the Philips bulbs - it could be a manufacturing defect since only one headlight seems to have an issue. When one of these give up the ghost I will probably try another set of the same just to see.
My father changed his car and I fitted Ring Xenon Max bulbs in both the dipped and main beams and he was very impressed but this was going from standard halogens.
I was also in front of my old car (now owned by my sister) fitted with Ring Ultra Xenon bulbs and could not believe how bright and white they were - I had to ask if she had main beam on but apparently not!
Update 22/10/11: One of the Ring Xenon Max bulbs blew recently but since the car is due to go back under the lease agreement I have just put any old bulb I could find in - probably an 2nd hand Ultra Xenon, who knows! I did notice on the bulb I took out that the silver coating on the end of the bulb was starting to flake off and was not very uniform - first time I have seen this happen in the many bulbs I have fitted. It's been just over 12mths since my last update, so the Ring Xenon Max's have lasted a decent amount of time. I've already got my next set of bulbs lined up for my replacement car - I'm going for Osram Night Breaker Plus's in the dipped beam as they got a very good review again in the latest round of 2011 tests, Ring Xenon Max's in the main beam and some yellow xenon bulbs for the fogs. Unfortunately because it's going to be a different car I won't be able to do a direct comparison between the Ring Xenon Max's and the Osram Night Breaker Plus's but I'll test against the standard OEM bulbs first.
I have to note that these uprated bulbs seem to have most upgrade benefit if you have reflector headlights rather than the increasingly common projector lamps (polyellipsoidal - the ones with the lenses in them) - it does improve these types of lights but just not as much. Note: This is just my personal opinion.
There is a good article on "headlamps" on Wikipedia as a reference for further reading.
Some other things to be aware of:
a) Keep the headlight glass clean - you'll be amazed how a quick wipe will improve the light output no end.
b) These bulbs seem to blow more often, probably due to the higher output and/or the construction of the bulb itself.
c) Check when fitting new bulbs to make sure they are located correctly in their holders.
d) If you change to xenon headlight bulbs you may want to change your sidelights too, but beware of cheap, no-make LED bulbs, their light output is generally low, not very white and tends to be in one direction only (although this situation is now improving). Update 13/09/10 - Important: When fitting LED lights to new cars this can result in bulb blown indicators on the dashboard - this is due to the low power consumption of LED's, so you you need canbus error free LED lights (search for "canbus led" or "error free led"). Also if the bulb doesn't seem to work try turning the bulb around 180 degrees - LEDs are directional so you may have in the wrong orientation.