In article s.com,
(Robert Bonomi) wrote:

All incandescent lamps use tungsten filaments. There are some trace
elements added that tend to prolong life but that material is not
altered for different voltages.

Halogen lampsd have one of the halogen gasses in the envelope. This
creates a "halogen cycle" where the evaporated tungsten combines with a
halogen gas molecule and then breaks down when the combined molecule
strikes the filament again. Thus the lamp can operate at a higher
temperature before failure.

Dick


Frequently, however, the higher voltage bulbs are made with a somewhat
_different_ (higher resistance) composition of material for the filament.

Allowing the filament construction to be thicker than the 120V
'counterpart'.
This improves the mechanical stability, and the ability to withstand
shock
and/or vibration.