What are the differences between LHD and RHD headlamp units, apart from the lenses? There's a common belief that converting from one to the other takes more than a change of lenses - is that true? Or are parts dealers just talking us into buying whole assemblies when only the lenses are needed?
LHD v RHD Headlamps
- Thread starter tat
- Start date
Dave Wilkinson
New member
Tat,
They are very definitely TOTALLY different!!! The LHD headlight units are completely different to the RHD units - and changing the lenses isn't enough. I have been in the situation where my car failed an MOT beam pattern test with RHD lenses on LHD units and had to replace the whole headlamp units for it to pass with ease. Many on this forum and elsewhere will tell you that changing lenses (or even sticking black triangles on the lenses) is enough to get you through an MOT - believe me, a bent examiner is all you need, but nothing but the real deal will help you meet the letter of the law.
Regards
Dave
They are very definitely TOTALLY different!!! The LHD headlight units are completely different to the RHD units - and changing the lenses isn't enough. I have been in the situation where my car failed an MOT beam pattern test with RHD lenses on LHD units and had to replace the whole headlamp units for it to pass with ease. Many on this forum and elsewhere will tell you that changing lenses (or even sticking black triangles on the lenses) is enough to get you through an MOT - believe me, a bent examiner is all you need, but nothing but the real deal will help you meet the letter of the law.
Regards
Dave
I too had tried swapping just lenses (on a 1989 930) and got a strange beam pattern - definitely not the same pattern as you get from UK sourced RHD headlamp units. However, I've not found anyone who can tell us exactly what the differences are (apart from lenses). I'm wondering if the strange beam pattern is a result of not fitting the replacement lenses correctly, or inverting the bulb (is that possible?).
tat
tat
Dave Wilkinson
New member
Tat,
I'm afraid I'm no lighting expert, but I can imagine that there are a lot of design considerations when developing a light unit. The lens itself plays a part but the nose cone reflector (in front of the bulb) and the main parabolic reflector are the prime movers when it comes to the beam pattern. Given that the RHD beam pattern is considerably different from the LHD beam pattern I think it would need an eternal optimist to hope that it was ONLY the lens which differed.
It isn't possible to invert the bulb because the H4 bulb has three locating lugs which will only allow the bulb to mount the correct way up. The bulb also has an internal reflector which diverts the beam from the dipped filament into the main reflector from a diffrent angle helping toproduce the cut off, left biased beam.
I'm sure someone with more of an insight into headlamp design could elaborate further but I think you're safe in assuming there's more to it than just the lens.
Regards
Dave
I'm afraid I'm no lighting expert, but I can imagine that there are a lot of design considerations when developing a light unit. The lens itself plays a part but the nose cone reflector (in front of the bulb) and the main parabolic reflector are the prime movers when it comes to the beam pattern. Given that the RHD beam pattern is considerably different from the LHD beam pattern I think it would need an eternal optimist to hope that it was ONLY the lens which differed.
It isn't possible to invert the bulb because the H4 bulb has three locating lugs which will only allow the bulb to mount the correct way up. The bulb also has an internal reflector which diverts the beam from the dipped filament into the main reflector from a diffrent angle helping toproduce the cut off, left biased beam.
I'm sure someone with more of an insight into headlamp design could elaborate further but I think you're safe in assuming there's more to it than just the lens.
Regards
Dave
]Thanks for all the comments! I've been getting by with stickers on my LHD lenses, but it's about time I did something more permanent! Sounds like it'll be safest to replace the whole units - then there'll be no question about them being legal.
Agree that 911 headlights are pretty poor at the best of times!
tat
Agree that 911 headlights are pretty poor at the best of times!
tat
Guest
New member
I used to work for an automotive lighting company years ago so can add some theory.
The main issue is - is the reflector parobolic, virtually all pressed metal ones are whereas most of the plastic ones are not. if it is parabolic then it does not contribute ant difference to LHD RHD.
The lenses on our cars are definately different. Some other makes do have symmetrical lenses that can be used eithe left or right.
The last element is the bulb which is the missing link from the previous discussion. If you look at the H4 bulb you will see that there is an intenal light shield (little dish) for RHD thats us this dish is rotated about 15 degrees upwards to the nearside. For LHD it is rotated the same ammount the other way.
On other cars with symmetrical lenses the bulb housig has a method of rotating the bulb for either hand driving.
As for those of you who have just changed the lenses either don't complain of crap headlights or stay in at night.
The main issue is - is the reflector parobolic, virtually all pressed metal ones are whereas most of the plastic ones are not. if it is parabolic then it does not contribute ant difference to LHD RHD.
The lenses on our cars are definately different. Some other makes do have symmetrical lenses that can be used eithe left or right.
The last element is the bulb which is the missing link from the previous discussion. If you look at the H4 bulb you will see that there is an intenal light shield (little dish) for RHD thats us this dish is rotated about 15 degrees upwards to the nearside. For LHD it is rotated the same ammount the other way.
On other cars with symmetrical lenses the bulb housig has a method of rotating the bulb for either hand driving.
As for those of you who have just changed the lenses either don't complain of crap headlights or stay in at night.
Dave Wilkinson
New member
Tat,
Not true. The reflectors referred to above are part of the main reflector assembly - not the bulb. H4 bulbs are H4 bulbs - there is no difference between LHD and RHD, the difference is in the reflector mounted ahead of the nose of the bulb inside the main reflector. If you look through the lens you will notice that you cannot see the tip of the bulb - it is hidden behind the reflector in question.
I think there is more science behind this question than many would appreciate and I think Nigel has hit the nail on the head with his post above. It's very easy to assume that a headlight is a very simple device and I think you will find that very far from the truth.
Perhaps much of the comment about 911 lights being "crap" might stem from the use of wrongly converted lights. I have to admit that my new RHD lights with Halfrauds +50% bulbs aren't that bad - not up to BMW Xenon performance, but not bad.
Regards
Dave
Not true. The reflectors referred to above are part of the main reflector assembly - not the bulb. H4 bulbs are H4 bulbs - there is no difference between LHD and RHD, the difference is in the reflector mounted ahead of the nose of the bulb inside the main reflector. If you look through the lens you will notice that you cannot see the tip of the bulb - it is hidden behind the reflector in question.
I think there is more science behind this question than many would appreciate and I think Nigel has hit the nail on the head with his post above. It's very easy to assume that a headlight is a very simple device and I think you will find that very far from the truth.
Perhaps much of the comment about 911 lights being "crap" might stem from the use of wrongly converted lights. I have to admit that my new RHD lights with Halfrauds +50% bulbs aren't that bad - not up to BMW Xenon performance, but not bad.
Regards
Dave
Guest
New member
Gee, thanks.
My beam pattern is 100% fine with just new lenses, have Osram Silverstar bulbs and upgraded headlamp wiring with relays taking current direct from the battery rather than routing it through the switch, better than stock but still not bright enough for me. It's a common enough complaint on old 911s.
I will put HIDs on my new one which will completely resolve the issue according to those that have done it. Perhaps worth considering for anyone looking at buying complete new headlamp assemblies, can't be much in it money-wise over the life of the car and would add value in resale if the buyer knows their stuff IMO.
Don Curtin
New member
Hi
I have a left hand drive and it came with right hand lens.Always passed MOT but lights v/poor.
Changed the headlights to proper right hand ones and beam pattern much inproved.If you what to drive at night at any speed,spend the money and do the job properly. I asked around and the shape of the reflector is different .
I have a left hand drive and it came with right hand lens.Always passed MOT but lights v/poor.
Changed the headlights to proper right hand ones and beam pattern much inproved.If you what to drive at night at any speed,spend the money and do the job properly. I asked around and the shape of the reflector is different .
Guest
New member
The majority of my night driving consists of blatting around the back lanes of LeMans in the wee hours. I'll stick with my LH headlights where they're perfect abroad as they were meant. Uk MOT - stickers on the lenses get's it through no problem and I've used a selection of different garages over the 4 year's I've had the car. Plus I seem to be getting worse at this originality bug and don't want to change them - yes, silly I know.....
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