A 12V bulb doesn't care whether it's running on DC or AC. You wouldn't get the higher turn-on peaks with DC that you get with AC so it'd be less likely (but not impossible) for it to pop at turn-on. But don't forget that a car battery is really something like 13.6V, a bit higher with a charger running. Bulb life goes inversely with the twelfth power of the voltage so the lifetime would be reduced by 80% running at 13.6V relative to 12V.
Originally Posted by Ken Nadvornick
A 120V bulb running on 12V would be very dim indeed, but would probably outlast your great-grandchildren.
I've gotta build that zero-voltage-switch thing, maybe over Christmas as my employer kicks us all out for two weeks.