These are LED lights called fuse lamps that are 8 volt and will plug into a florescent light holder. They are incredibly bright as they have 3 lights. These are warm white and are 7 for $7.99 on ebay. (They're cheaper through the consumer electronics section than sold as dollhouse components.)
The holders are called flourette sockets on the Cir-Kit page. There is a nail version (first photo) and a solder version. Of course these use the traditional 12 v bulb which is $2.48 each.
The light holder pushes into the tape run. The LED light can be used with a 9 volt battery but the more lights you use, the less life in the battery.
You might be able to use 12 volt - but not sure if it would burn the light out. You could solder the 9-volt battery holder wires into a tape run. Or you can get a 9-volt transformer. Many transformers for household items will offer different voltages. You can often find these at second hand stores, too.
I haven't tried this idea yet, but may get some more of these LED lights and try it out. I'll post if I do. Let me know if you decide to experiment.
I also found this LED light at Oakridge Hobbies which looks similar but is a flat shape instead so it doesn't need a holder. There is no information on voltage. It looks like it has wires on each end, which would solder in or attach is my guess. It's $7.89 (sale).