Originally Posted by
BarracksSi
I've had a hard time reading street signs while in my car, and it has a less-defined cutoff than the one pictured. My symmetrically-beamed bike lights light up the same signs just fine.
Ok, construct your own cutoff and go do some real-world observations in darkness, like I did. Report your own findings. I think you'll see the same thing I did: a given amount of light coming from a small aperture makes it effectively intense. I don't see easy ways around that without using very large lenses and reflectors, which isn't going to go over well on bicycles. You know what they say about theory versus practice
1) Not always possible, so that tidbit of advice doesn't apply.
It's always possible where I live. I consider our own MUP to be very poor in design anyway. It's also technically off-limits after dark. The last time I rode it, I was clocking 20-24mph (first leg of a nighttime century) with a 700-lumen light at full power, and really wouldn't want much less than that, since it's narrow, with cutesy-pie twists and turns, and an unmarked edge that drops 3 inches into loose gravel in most places. Once I got off the stupid MUP onto nice normal roads with fog lines, yeah, I could drop it to 175 lumens in relative safety.
If I had no option but to ride the MUP, with fair amounts of oncoming riders and unlit pedestrians, there would really be no option but to throttle back my riding speed. Maybe then I could scrape by with a feeble light, aim it down 20 feet in front of the bike, and try to stay away from the edge. On an average day, how many oncoming cyclists are you guys encountering, anyway?
2) All it takes is a flash to ruin your night vision. The difference is that "badly aimed, annoyingly bright" lights are so bad that, until they finally pass, you can't see the ground at all unless you block them from your face and shine your own light straight down.
This touches on another problem with using an MUP in darkness. Some of the trail users are in full night-vision mode, and someone with a small be-seen bike light is pretty close to that. Even the OP's small 3W light will ruin the night vision of a pedestrian with no lights at all. What are we supposed to do, all ride ninja? You have to draw the line somewhere. I could dim my light system to 25% power, aim it down and swing it sideways, and SOMEONE would still probably gripe.
Exposure to relatively bright lights is an inevitable part of using public roads and paths. At the last turn on my homeward commute, I face two lanes of cars with their low-beams aimed right at my face (humped intersection). That's not their fault.