I have found this or that forum post about using an aspheric lens, but I have questions, as most of the threads were related to making a thrower. It seems we are all reasonably close to this (though I'm not sure if we have [or the Convoy L6 specifically has] an elliptical or parabolic reflector):
My goal is this here, for use on a bicycle:
Does anyone have any speculation or experience with creating that sharp cut-off on a flashlight so that it can be used on a bicycle trail without dazzling or blinding other riders? I used the Convoy L6 at ~19 amps and it causes people to wreck (or just dismount the bicycle and wait for me to pass) as much as 100's of meters away! I already have 3 or 4 convoys, and would like to modify one into a projector instead of trying to buy a bicycle light (that won't have nearly the lumens/output of an L6.) Seems all I need is a suitably-sized aspheric lens with half the plano side taped over to create the cut-off, but would like any input before I attempt.