How many lumens do I need in a headlamp?

It depends on the task. For around-camp use, reading, and general chores, 200-400 lumens is plenty, which covers most of the compact models here. For trail running, mountain biking, or anything where you need to see far ahead at speed, look toward 800 lumens and up, the Fenix HL18R-T (800lm) and Coast XPH34R (2700lm) sit at that end. Higher lumens almost always mean shorter runtime at max output, so check the runtime spec, not just the headline brightness.