Originally Posted by hamster

USB is de facto standard for midrange lights. Cheap lights use batteries because they are weak and they can last a while on standard batteries without burning a hole in your pocket (one AA battery is 3 Wh, 2 AA batteries will power a 60 lumen light for 6 hours.) High end lights require custom chargers. In the middle, it's all USB.

150 lumens per watt is a spherical cow, you don't see those outside labs or theoretical papers. 60 lumens per watt is what you see in the real world.