what filament? halogen bulb no have filament.
and 50/220= 0.227 , so how do u compare? or u make faulty calculation?
True purpose of 12Volt bulb is if u have a 12volt connection, then u can use it. No difference in light.
if u want less light, u buy lesser watt bulb. changing voltage makes no difference except u use according what ever power connection is available.
if that 12V bulb is DC supply requirement one, then its obvious that it was made for use in automobiles etc etc..and places where 12V DC power is available.
If u use 12V AC supply bulb in common house hold power supply, chances are something in it will blow up.
The common household power is normally 50hz, 240V ( or maybe 220 ).
So use bulb according to that only. that will money.
in short, power requirement/consumption for 50watt input rating bulb regardless of voltage is same.