I've been looking around for outdoor flood lights to make into a bike light. I've read through a lot of the Total Geekiness thread but I'm still confused with something - if I buy a light that uses a 20 watt 12 volt MR-16 lamp, won't it be using an AC current? If I have a lead acid battery (cheapest option), how can I get the lamp to work?

This may be some completely stupid question, I know but I'm pretty much a noob at this stuff.

Thanks in advance