Nothing significant. Depending on how much of a fluctuation exists, the
brightness may change in response to it, but aside from that... <shrug>

When you get right down to brass tacks, a halogen bulb is nothing more
or less than your basic incandescent filled with a fancy gas mixture
that's supposed to keep the metal that boils off the filament from
plating onto the glass/quartz/whatever-material-it-happens-to-be
envelope and dimming the bulb. A side-effect is increased life, since
the gas mixture is supposed to drive the stray metal atoms (that would
have plated onto the envelope) that have boiled off it back onto the
filament, preventing filament erosion/breakage. All an incandescent
"cares" about is that there's enough voltage to overcome its resistance
and allow current flow, and enough current to heat the filament to it's
"glowing" range. Beyond that, voltage/current are pretty much irrelevant
unless you get into the realm of "stupid-huge" voltage/current numbers.
With the halogens, they need to run in their designed temperature zone
to get the benefit of being halogens, but even if underdriven, they
should produce plenty of light - They'll just be a "more expensive
incandescent" otherwise. AC versus DC is a non-issue for them - Given a
bulb suitable for the voltage being used, you should see zero practical
difference whether the juice is AC or DC. Flourescents or LEDs, on the
other hand, are sensitive to AC versus DC issues, either not functioning
at all, or functioning poorly. Likewise, arc (discharge) lamps - Some of
those are polarity-sensitive, others don't care what the polarity is, or
even if it's AC or DC.

Unlikely. It's just your basic step-down transformer, *POSSIBLY* with a
rectifier and voltage regulator. As long as the voltage/current is
reasonably correct (and "reasonably correct" is a pretty big target)
it'll light up. Go ridiculously over voltage, and you may find the bulb
developing thermal problems, or just plain "blowing out" when powered
up, but unless there's a fire issue involved, not really a big deal. Go
under voltage, and it's either not going to light, or light only dimly,
at best. Again, no big deal.

Dunno... why do you want a mega-bulb inside the car? That would have a
bearing on alternate ideas.

Why would one need that much light (50-watts) inside their car?

Don't those get pretty hot? Hot enough to melt the dome light's plastic
mount?  (& I know we're not talking those floor-standing halogen lights)

One question for you -> can the light handle being in a car or will the
first bump reduce the filament to chunks?  Might be worth testing - plug
one in and shake it around a bit to see if it can handle the abuse.

(I'm thinking rough service bulbs for trouble lights vs regular bulbs.)

You might be better off with a cheap driving light in the car.
(and some sunglasses)

Ray

[snip]

Look for a 12V fluorescent fixture. Much lower power consumption for the
same light output.