One of the issues I've always *thought* existed with stuff pulled from an
auto is that you may also need to use the headlight lens that came with
the
car, because the lights themselves only include a reflector, bulb, and
ballast, but not an optic. I think a Lexus (tm) headlight lens assembly
would look pretty unusual on my RV-6. ;-)

That raises some interesting questions, and I admit that I have not looked
at any to the automotive HID units with that in mind, or attempted to
dissassemble them. In theory, however, some cutting would be required,
since I believe that they are made to conform to the definition of sealed
beam.

As far as I know, the definition of a sealed beam lamp is that the external
lens and the reflector are "manufactured" as a single unit--which can not be
dissassembled and reassembled in the normal course of service. A carefull
look at some of the halogen headlamp assemblies on some of the less
expensive newer cars suggests that it would also be technically correct to
glue/bond a plexiglass lens onto one of the older style sealed bean headlamp
bulbs, as a secondary manufacturing prosess--thus creating a streamlined
sealed beam headlamp.

All of that is a, possibly long winded, way of suggesting that the HID
headlamps on cars sold in the US might simply be a permanently glued version
of more fully maintainable headlamp assemblies sold elsewhere. In other
words, we may simply be giving up the ability to replace the plexiglass
outer lens in order to comply with laws mandating sealed beam lamps.

Therefore, the possibility exists that the outer plexiglass lens could be
cut away from some of the HID headlamp assemblies, and that sufficient
structure might remain to support all other portions of the
assembly--including the primary focussing lens. A new plexiglass lens could
then be a part of either the airframe on the lamp assembly--since there is
no sealed beam requirement for an aircraft.

Some of the HID headlamp equiped cars are getting old enough for the outer
lenses to cloud over in the southern parts of the US, so some assemblies
could be available from salvage yards at very reasonable cost--depending
upon the cost and longevity of the light and balast. The beam width,
however, will be *much* greater in the horizontal plane--which could be an
advantage for taxiing.

If anyone has occassion to try any of this, I am very curious as to the
result.

Peter