Not to bring back this zombie thread, but I tried the halogen bulb and it worked, but it was rather dim. I believe Vistas were designed for 12V, and the bulb is rated for 5W, so the 6V 3W from my dynohub worked but was a bit underpowered. Reading the forum last night, I found this post, where funkystickman uses a LED halogen replacement. I thought I would try a similar, though smaller, LED bulb for an MR11 Halogen: http://www.dealextreme.com/p/mr11-1-...b-11-18v-91948

Of course, I'm curious how much light it will produce at 6V and if it will work on AC. At worst, I'm only out $4. Anyone tried one of these bulbs?