I read an article online that was very in depth and thorough about fly fishing at night. It covered a lot of the "safety" issues and things you should and should not do. One thing I remembered reading was about a certain color headlamp/flashlight color so you would not spook the fish.
I have never fly fished at dark but have fished plenty bass tourneys and fished for crappie at night. I think it would be pretty fun and interesting fly fishing at night. I will try to find that article again.