P43t to P45t adapter questions

furgo

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I've been looking at upgrading my R2 P45t headlight bulbs to H4 P43t ones on my R2 headlight assembly. I'm aware that there are H4 lamps with P45t mount, but there are not as many options available as H4 P43t lamps. So I've found out there seem to be P43t to P45t adapters such as these, or those from alternative manufacturers.

That'd be a perfect fit. Yet doing some more research, there seem to be some claims that these adapter are not optimal. For instance, in this forum:

No. There is no way to make a regular H4 bulb (with its P43t base) fit or work correctly in a lamp designed to take R2 bulbs (P45t base). There are "adaptors" around -- they don't work.

Source: http://www.candlepowerforums.com/vb/showthread.php?347775-R2-vs-regular-h4-bulbs

Likewise, I'd advise against buying lens/reflectors that take the P45t bulb fitting (locates in the reflector with a series of lumps and bumps); fitting a P43t bulb with a "P43t to P45t adaptor" makes for a poorly-focussed bulb.

Source: http://www.triumphrat.net/classic-vintage-and-veteran/636402-brighter-headlamp-2.html

The P45t to P43t adaptor rings don't work -- they fail to put the bulb's filament in the correct place relative to the optic, and so the beam focus is grossly upset.

Source: http://www.st1300.us.com/showthread.php?t=357

2. Lens/reflector and bulb makers go to great lengths to ensure any bulb is on the focal point of any lens. Using the adapter (just so you can use the 'wrong' bulb) could move the bulb off the focal point of the lens, and you'll end up with the dreaded 'black hole in the middle of the beam'.

Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread

In summary, the adapters reportedly put the filament of the H4 P43t bulbs in a non-optimal location relative to the reflector, which results in an equally non-optimal focus point. However, there is no mention of by how much or in which way, and whether that could be corrected somehow. Particularly the latest statement mentions "could move the bulb off the focal point", which would indicate there has been no testing made to back these claims.

On the other side of the fence, one of the final replies from that last thread states:

To update, I have been able to test a selection of P43t H4 bulbs using adaptors in place of P45t H4 bulbs-which resulted in no apparent changes to the headlamp's beam pattern or focus, so as far as I'm concerned the adaptors do seem to work OK.

Source: http://britbike.com/forums/ubbthreads.php?ubb=printthread&Board=23&main=42437&type=thread

And also http://dastern.torque.net/Mods/H4mod.html shows a mod to drill some recesses on an R2 headlamp fitting to accommodate the 3 tabs of a P43t bulb. That would locate the filament more or less at the same position as the adapter (perhaps 1-2 mm more into the reflector). No mentions of

That same page points at how tilting the bulbs can affect focus (http://dastern.torque.net/Mods/H4tilt.html), but there is no mention of what the optimal filament distance to the reflector is.

Finally, looking at side to side pictures of H4 P43t + adapter vs. R2 P45t, it appears to me that the filaments sit at the same height in both bulbs –roughly, the filaments are shaped differently. I'll try to post some pictures when I've removed the bulbs from my car later on.

In any case, given that this forum is where the experts live, I thought they could shed some light into this (no pun intended!).

Thanks!
 

-Virgil-

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Those "adaptors" do not work. They really don't. It's a lovely idea, but an unworkable one. It's not about being "not optimal", which is sort of a hedge-y way of saying "I really really really want them to work, please, can't they work even just a little bit?" The answer is no. Or let me do some hedging of my own: I have tested about a dozen different variants of these so-called "adaptors" over the years, including the one you linked, in somewhere between thirty and fifty different headlamps designed to take P45t-base bulbs, and the results have always been one of these two: either the adaptor makes it impossible to lock the bulb into place (fail), or it can be locked into place but the beam pattern is destroyed (fail).

In summary, the adapters reportedly put the filament of the H4 P43t bulbs in a non-optimal location

The wrong location.

which results in an equally non-optimal focus point

Which results in a random spew of light, rather than a beam pattern.

However, there is no mention of by how much or in which way

It's a fraction of an inch, and it doesn't matter; move the filament a couple thousandths of an inch in any direction from where it's supposed to be, and you start screwing up the beam pattern. This is why filament position specifications are on the order of +/- 0.3mm, +/- 0.25mm, +/- 0.4mm types of figures. You go moving the filament a sixteenth of an inch (1.59mm) rearward with one of these "adaptors" and it's all over.

and whether that could be corrected somehow.

No.

Particularly the latest statement mentions "could move the bulb off the focal point", which would indicate there has been no testing made to back these claims.

That thing about "could move the bulb off the focal point" was made by someone who grasps that there's a problem, but doesn't have the expertise or experience to state it with the correct level of certainty ("will", not "could"). As far as tests, we also don't have to do tests to know for sure that triangular tires don't work even if you find an "adaptor" to put them on round wheels.

On the other side of the fence

...are people who don't know what they're talking about and really don't have any business commenting on this question.

And also http://dastern.torque.net/Mods/H4mod.html shows a mod to drill some recesses on an R2 headlamp fitting to accommodate the 3 tabs of a P43t bulb.

No, that page/procedure does not involve P45t (R2) bulbs at all. It involves a 45/45-watt variant of the H4 bulb used by Honda in some of their US/Canada-market motorcycles. The base is identical to a regular H4 bulb's P43t base, except the tabs are placed differently around the circumference. That's nothing like the situation with P45t (R2) bulbs.

That would locate the filament more or less at the same position as the adapter (perhaps 1-2 mm more into the reflector)

There is nothing about the Honda bulb mod at that page that would put the filament anywhere except exactly where it's supposed to be.

there is no mention of what the optimal filament distance to the reflector is.

That's not a piece of information that would be useful or usable in the field. It's of use when engineering a headlamp.

Finally, looking at side to side pictures of H4 P43t + adapter vs. R2 P45t, it appears to me that the filaments sit at the same height in both bulbs –roughly

Your last word there is the problem. Refer to the tolerance figures (less than a millimeter) above. "Roughly" doesn't begin to cut it, and we don't measure these things by eye.

In any case, given that this forum is where the experts live, I thought they could shed some light into this

It's already been shed...now all that's left is reconciling yourself to the reality that what you want to do just isn't a good idea.

Perhaps there's a work-around in the form of a headlamp that fits whatever kind of bike or car you're working on and accepts H4 bulbs.
 

furgo

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Thanks for the detailed reply.

[...] I have tested about a dozen different variants of these so-called "adaptors" over the years, including the one you linked, in somewhere between thirty and fifty different headlamps designed to take P45t-base bulbs, and the results have always been one of these two: either the adaptor makes it impossible to lock the bulb into place (fail), or it can be locked into place but the beam pattern is destroyed (fail).

It's a fraction of an inch, and it doesn't matter; move the filament a couple thousandths of an inch in any direction from where it's supposed to be, and you start screwing up the beam pattern. This is why filament position specifications are on the order of +/- 0.3mm, +/- 0.25mm, +/- 0.4mm types of figures. You go moving the filament a sixteenth of an inch (1.59mm) rearward with one of these "adaptors" and it's all over.

I am personally fine with understanding why they don't work, which will help me make an informed decision not to get the adapters and get some H4 headlights assemblies with P43t fittings instead.

So far all the information I could find were statements such as "it doesn't work", "it works for me" or "no complaints from customers so far" (I did contact one of the manufacturers). Some folks on another forum mentioned there were "rumours" these adapters did not work. Your replies above are the first time I hear facts being referenced.

Would you happen to have a record of your test results, or the source for those tolerance figures you mention? I'm not trying to be picky here, I simply think having the actual facts and directing folks to this thread would help putting this matter to rest.

No, that page/procedure does not involve P45t (R2) bulbs at all. It involves a 45/45-watt variant of the H4 bulb used by Honda in some of their US/Canada-market motorcycles. The base is identical to a regular H4 bulb's P43t base, except the tabs are placed differently around the circumference. That's nothing like the situation with P45t (R2) bulbs.

Ah, indeed. I stand corrected, thanks for clarifying that and apologies for the confusion.
 

Alaric Darconville

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there seem to be some claims that these adapter are not optimal.
"Not optimal" would be preferable to "doesn't work". This adapter is not simply "not optimal"; the adaptor doesn't work.

In summary, the adapters reportedly put the filament of the H4 P43t bulbs in a non-optimal location relative to the reflector
Again, it's not "non-optimal"-- it simply is wrong. If you move the filament .2mm in any direction from optimal, that would be "non-optimal". If you move it 1.59mm in any direction, that's no longer "non-optimal", that's plain and simple WRONG.

A terrible analogy: Putting butter in the freezer is "non-optimal". Putting butter in the toilet bowl is wrong. The first method makes the butter hard to spread, the second method means you're not seriously going to put that on a sandwich, are you?

That same page points at how tilting the bulbs can affect focus (http://dastern.torque.net/Mods/H4tilt.html), but there is no mention of what the optimal filament distance to the reflector is.
The optimal distance is the distance the filament of the correctly-chosen light source (that is, the light source the lamp designer picked) is when that correctly-chosen bulb is correctly installed in that lamp. This is why lamp bases are keyed and everything is set up so that if the bulb is installed correctly the filament is where it needs to be. You go using "adapters" and the wrong bulb, you take a working lamp and make it non-working.

Finally, looking at side to side pictures of H4 P43t + adapter vs. R2 P45t, it appears to me that the filaments sit at the same height in both bulbs –roughly, the filaments are shaped differently.
"Roughly". Again, the precision involved with making a filament bulb is such that "roughly" is useless. Two pushrods taken out of an engine can look "roughly" the same, but if you trade their positions in the engine it changes the valve lift to a large degree. If you swap bolts between to M16 rifles it can have disasterous effects on the both of them-- even though they look "roughly" the same or even absolutely identical to the eye. We don't have that kind of precision in our eyes for this sort of thing.

So far all the information I could find were statements such as... "it works for me" or "no complaints from customers so far"
People making statements like "it works for me" have no business determining what works for them. The "no complaints from customers" is even more worthless than that. It's not information, it's noise.
 

Alaric Darconville

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Would you happen to have... the source for those tolerance figures you mention?
49 CFR Part 564 Replaceable Light Source Information.

Bulb types are described, and for such bulbs described you get such goodies as "permissible offset of filament axis", "bulb eccentricity", and all sorts of things. For an H7 bulb to be a legitimate H7, for example, the ends of the filament must lie between particular set of points. The envelope must be free of optical distortion in a particular degree range. The dimensions of the PX26d base is defined. Everything is well-defined here-- you'll not see "roughly" or "works for me" in these specifications.
 
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