Originally Posted by mechBgon

I've done photos and firsthand observation of my own lights, including ones I was attempting to devise a true beam "cutoff" for. Based on my observations, including video testing, a bright bike headlight isn't going to look a lot different when aimed down and to the right, unless you point it so far down that it's basically pointless to see forward with. The problem is that a lot of light is coming from a small source, and therefore it has high intensity per unit area. Compare the size of a 200-lumen bike light to the size of a ~1000-lumen automotive headlight lens... the difference in effective surface intensity must be approaching two orders of magnitude.

My solution: ride on roadways. If you're coming towards me, you're 10-20 meters to my left.

Oh, and the beam cutoff, as nice as it looked when aimed at a wall, was visually indistinguishable from the same light without a cutoff, at a range of about 50 meters. Sounds good, doesn't really work.