Are you trying to do something like this:
You can get this effect two ways. The ones in the picture are done with tape LEDs under a clear plex ring with a sanded finish. The other way is done by bending clear plastic rod with cuts every 1/2" or so, it's described on a webpage, search for BMW angel eyes do it yourself.
You do not need any transformers with the tape, they run on 8-13.5 volts. The individual LEDs used in the angel eyes require resistors.