I had a DiNotte 200L (200 Lumens) and it barely cut it. I mean, the optics might have something to do with it... throwing photon from hither to yon without a really good focused area on the road. I'd outrun my light (going too fast to stop in time for a hazard exposed by my light) at maybe 12 MPH on a clear night on the dark backroads. I can see maybe 500-600 lumens being sufficient, but 256 doesn't seem like enough to me.
You're right -- the optics are everything. The flashlight fetishists love round symmetrical beams, which is exactly what you don't want in a headlight.
You want to focus almost all of the light at the horizon, with some spill below and a sharp cutoff above. Anything else is wasted. See: http://peterwhitecycles.com/plight.asp
I agree. It's just hard to find good headlight-worthy optics for DIY LED or Halogen lights. You always have to buy the whole package, always for $too.much from someone like Peter White, or the local bike shop.
Even my "good" headlight (15W, ~300 lumens by my guess) is just a stupid 6V MR11 bulb with a clear waterproof lens in a waterproof housing. No optics. It's just a farking accent light that can be bolted to a bike. Über lame.
