There are few choices of 6V LEDs but they are available. Be aware that most are directional and from what I've seen personally the number of LEDs makes a difference. (more LEDs = more light) I use
these and I'm quite pleased with them. They light the whole taillight & have substantially more LEDs than the other bulbs I've seen. You can get cheaper bulbs but the ones I've seen have fewer LEDs and are directional so they provide a "hot" red spot in the middle of the lens instead of lighting the whole taillight. 4ontheFloor was working on a project for making 6V LEDs but I'm not sure of the status.
