12vdc is it on a vehicle.
If it is in a house this it is either 120vac or uses a transformer/inverter to become 12vdc.
Personally if you have a vehicle and are planning lighting or changes to lighting I would got to LED and save the max power possible. Longer battery life, less concern over wiring and lower heat creation.
There are plug in LED lights for almost all RV style fixtures and if not then contact one of the LED places on the web and they should help you put something together.
The three brass fixtures (w two 12 volt halogen light sockets in them) that are in my van came wired for 120 volts ac. They had a 10 to 1 step town transformer in them to make 12 volts ac. I cut out the transformer and re-wired the lights. They work fine on 12 volts dc. One point though: the lights had a SLIGHT dimming switch position that failed after a few trips. The resister or what ever was providing that feature was designed for TWELVE VOLTS and the van batteries are often at 13-14 volts. Other than that miner loss they work fine.
Also buying the lights at Lowe's (USA) big box hardware store and converting them from home use to van use saved over 66% of the cost. RV specialty stores charge an arm and a leg for their low volume specialty 12 volt dc lighting.
In short 12 volt halogens do not care about ac or dc.
Yes that's it here in the EU we have 220-240 Volts but lots of lighting is 12 volts with a transformer... I will trial test some setup with a couple of motorbike batteries i have before I really get installing...
I am probably going to use LEDs for the light that I will have on longest... but for spot lights with short usage I might have the odd halogen...
I was unsure about the AC/DC issue
New ride: 2000 Chevy Suburban 1500 4WD 1998 Chevy Express 2500 past project
+ 1990 Mitsubishi Pajero V6 3.0l
+ 2001 Saab 9-5 Aero Hirsch
+ 1972 Saab 96 V4 (not running)
+ fixed house (Argh)