Been looking at doing the same thing myself. 12v automotive wire is inexpensive in bulk from someplace such as waytek wire, I've been meaning to drop a pair or two down through the wall in each room. I intend of taking the transformer and rectifier from an alarm clock and powering it straight from 12v as well as things such as my cell phone charger, just replace the wall wart with a regulator for whatever voltage the charger requires and eventually placing a solar cell on the house roof to charge the 12v battery. There are plenty of LED automotive replacement lamps as well. I bought some but founf them too dim and blue for dahs lights so I'm going to make some small lamps form them.