We may soon offer interchangable compact fluorescent bulbs and ballasts for both 12 volt DC and 120 volt AC systems. Currently, interchangable parts are available from Jade Mountain. I personally use 12 volt DC halogen bulbs for reading lights, while lighting whole rooms with compact fluorescents. These really are a very good, energy efficient method of area lighting, and are widely available. They are the most efficient room light available.
Problem is, the quality of light is very irritating to some people.
It's too blue, and the flicker is extremely annoying to me. But fluorescents make great energy efficient lights for shops, garages, etc. where you don't have to spend too much time in the winter. I also use them for under-cabinet countertop lights in the kitchen. They fit in ALL standard light sockets, so the monetary investment is low. AC versions are available anywhere, and are still more efficient than standard bulbs.