Powering halogen bulb

@allObjects Hello everyone. I asked in another thread about a halogen bulb to light a projector. A
particular DIY project site shows the use of a 12v 20w halogen bulb,
presumably, because that's what the projector they have puts out to the lamp
socket. However, apparently, mine, which uses 21V bulbs and I find that
when I test the socket, it actually shows about 24V.

The idea is to splice the halogen bulb on its own mounting into the wires for
the projector's lamp. However, I assume I can't run a 12v bulb on a 24v
source, if I can't find a 21v (or 24v?) 20-watt bulb, how would I go about
rigging (or finding) an independent 12v (or whatever voltage) power supply
for the halogen bulb?

Thanks