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Thread: What's wrong with projector retrofits?

  1. #1

    Default What's wrong with projector retrofits?

    [This thread has been made into a sticky for the reason that the question it addresses comes up frequently. -Mod]

    So what exactly makes HID projector retrofits so bad? The projector is basically a self contained unit, so as long as one places it in a clear lens headlamp, in a position reasonably close to what it would have been in on the donor vehicle, then it should perform just fine, no?
    Last edited by -Virgil-; 06-28-2014 at 04:17 PM.

  2. #2

    Default Re: What's wrong with projector retrofits?

    Quote Originally Posted by splew View Post
    So what exactly makes HID projector retrofits so bad? The projector is basically a self contained unit, so as long as one places it in a clear lens headlamp, in a position reasonably close to what it would have been in on the donor vehicle, then it should perform just fine, no?
    No. In just your two sentences here, you've explicitly skated right past three major problems, and that's not even the complete list. One at a time:

    The projector is basically a self contained unit
    Most projectors aren't self-contained. None of the ones found in original equipment headlamp assemblies are self-contained (that is, they're not sealed from water/dirt entry and they're unshrouded so they emit stray light in directions other than through the condenser lens; for these reasons they require being inside a housing. If the housing's not designed to hold a particular projector, in most cases the "alien" projector cannot be acceptably mounted in the "surrogate" housing. Certainly this is the case whenever the housing must be hacked in any way (cut, drilled, lens removed, etc); once that's done an acceptable environmental seal is never re-achieved. More about this alien/surrogate mounting issue below.

    There is such a thing as a self-contained projector. Hella, for example, has an extensive range of 50mm, 60mm, 90mm, and 120mm units. Low beams, high beams, low/high beams, fog beams...halogen, HID, LED...Right-traffic, left-traffic, etc. However, these don't erase the problems, they just change to a different set of problems. A headlamp is type-approved or certified to the applicable regulations in the form it's produced. Putting a projector, self-contained or not, behind a lens it wasn't specifically designed to be behind (as in an aerodynamic composite front light assembly from whatever vehicle you have in mind) means you no longer have a certified/type-approved lamp, you have an assemblage of parts that very likely does not perform the way the regulations require. This is not intuitive, but those lenses are not 100% transparent, and their surfaces are reflective. It is a very, very common occurrence during the design and engineering phase of an OEM headlamp that changes must be made (and remade multiple times) because while the optical package -- projector or reflector -- meets the requirements without the front lens, when the optical pacakge is put into the housing package including that front lens, the lamp doesn't comply. And an optics package that complies in one housing doesn't necessarily (often doesn't!) comply in another housing package, just because of differences in the size, shape, angles, and distance of the front lens and other elements of the housing. Typically the problems are insufficient intensity in the low-intensity zones (above the cutoff) due to less-than-full transmission through the front lens, and reflections within the headlamp bouncing stray light all over the place where it doesn't belong and isn't allowed. Highly trained and very well (and expensively) equipped engineers spend a lot of hours fixing these problems on each and every new project, because that is the nature of the job. It is not something that can successfully be tackled in a homeowner's garage, on a hobbyist's workbench, or behind the Retrofitz-R-Us website.

    in a position reasonably close to what it would have been in on the donor vehicle
    "Reasonably close" doesn't even begin to cut the mustard. Not only are there beam alignment issues (the high beam must be properly placed with respect to the low beam, and either it's right or it's wrong -- there is no such thing as "reasonably close"), but there are also center-of-mass/center-of-gravity issues. It is a lot harder than it might seem to devise a mount for a projector so that it stays put, doesn't shake, doesn't lose its aim, doesn't detach from its mounts. This, too, is something that practically cannot be done on a by-guess/by-gosh basis.

    it should perform just fine
    Headlamps are life-safety equipment. All aspects of their performance -- not just the beam patterns they produce, but also their mechanical and environmental robustness and, with HIDs and LEDs, electrical and thermal safety -- are specified in detail, objectively, by the applicable technical regulations. A wide range of performance and design are permitted, but the basic requirements are stringent and exacting. None of it can be assessed by eye. "Gosh, it looks good to me!" or "Wow, look at that sharp cutoff!" or "Nobody ever flashes me at night" or "I drive past cops every day and I never get tickets" just are not relevant responses to the real safety and reliability issues involved.

    It takes an enormous amount of money and a long time to design, engineer, tool, and test/approve/certify a legitimate headlamp. It's not because the people doing the work are slow-paced or lazy!

    Also read more information on "LED conversions" this, and here.
    Last edited by -Virgil-; 11-19-2014 at 07:43 PM.

  3. #3

    Default Re: What's wrong with projector retrofits?

    Well thank you for that detailed explanation. As for the "self contained" thing, I was referring to a projector with a proper shroud producing a correct beam pattern on its own, versus "hid kits" in halogen housing, which never produce a correct beam pattern. You brought up an important point I hadn't considered though, most HID projector retrofits are a bit haphazard in terms of mounting and environmental sealing. A few roughly placed screws and liberal amounts of epoxy seems to be all the work done on most.

    I also never considered the inner reflectivity of the housing lens either, that's interesting to know.
    Last edited by -Virgil-; 02-10-2014 at 08:33 PM.

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