I have been looking at a compact 500 lumen light from Lezyne that weighs 75g and fits under a bike computer. It is priced around $60. The runtime is a bit of a mixed bag: it can go for 35 hours on the lowest flash mode, but that drops to 1.5 hours on full power. It is compatible with action-cam mounts and supports external packs.
For those of you riding trails, is a light this small worth the sacrifice in runtime for the sake of a cleaner setup? Separate from the battery life, does the action-cam mount compatibility actually provide any practical value for your typical ride setup?
That runtime on full power seems a bit tight if you are planning a longer outing. For riding trails, I suppose you might use one of those LED headlamps used by campers instead. They tend to be a bit more robust and often give you more bang for your buck when it comes to battery life, even if the setup isn't quite as clean as a mount under the computer.
A camper headlamp sounds like a cheap way to get more runtime, but I am not sure how that holds up on a rough trail. If the light is bouncing around on a headband, it might be a distraction. The 1.5 hours on full power for the Lezyne is definitely tight, but I would rather have a clean mount and a steady beam than deal with a headlamp strap while trying to pick a clean line through the dirt.
Picking a clean line through the dirt requires a steady beam. A headlamp that shifts or bounces during a descent creates a moving focal point, which is a distraction you do not want when navigating technical terrain. A fixed mount on the bars is far more predictable, though 1.5 hours on full power is a gamble for anything beyond a quick loop.
That is exactly why the bar mount is the way to go. When you are trying to nail a clean line through the dirt, the last thing you need is the light beam dancing around because your head is moving. A predictable, fixed beam is a huge advantage on technical terrain. As for the 1.5 hours, it is a gamble, but for a quick loop it should be enough to get the job done without cluttering the cockpit.
Keeping the cockpit clean is definitely the way to go. When you are dealing with a compact setup, any extra bulk on the bars just gets in the way, especially if you have to maneuver through crowds or carry the bike up a flight of stairs. If it is just a quick loop, 1.5 hours is plenty; it is better to have a streamlined ride than a bulky battery you do not actually need.
