www.xenondepot.com if you need a kit. Don't know if they sell replacement capsules. One would think they should.
Because I ride a motorcycle, I am keenly aware of the need to make myself visible to other motorists, for safety. That same reasoning applies in the Prius and I use headlights on my Prius most of the time. If it's good weather, and I'm on an Interstate highway, I don't need the lights, so I turn them off. Head-on crashes are lethal, so running headlights on a two-lane road is automatic for me. Harry
Considering that few people can even see or hear the Prius I've been conditioned to believing that lights on is safer. That said... I know that few people can actually hear the Prius coming--it's an incredibly quiet car--so the lights may help. I've noticed that most people don't bother to turn on their lights when they're in tunnels, rain, etc. If I can barely see the car ahead of me, I doubt they can see me. The Prius is a smaller car--the SUVs can barely see that there's a vehicle near them; it might help if they might notice a glimmer of something before they cut me off again. I have similar issues with my 89 VW Cabriolet, which still gets 30-35 MPG, but remains a tiny tiny car.
Headlights Being a motorcycle rider myself, I always have my headlights on my bike and on the Prius. I agree, the Prius is a small car and sometimes it can be hard to notice its presence in the road. Safety is my top priority. I can just replace my HID lamps, if they burn out...
Use mine at night, when raining, and always always always when in the HOV lane. Keeping as visible as possible when there's such a big speed differential between me and the cars the next lane over could be a life saver.