Really nice. One problem I've thought of, though:
So, you go right and keep to turn it on, then go left to decrease the level. If you go left and keep, then you get the voltage warning, so that means you must go left multiple times- this may be a bit annoying to get to the lowest level.
==Yes. Not only getting down, but also getting up. Left+Keep=voltage, Right+Keep=OFF.
My personal way is: Setting default level at the 3rd or 4th lowest one.
That's 12mA or 50mA. When I need a bright ray, I always go Left directly to get tactical 700mA.
Also, IMO, there are slightly too many battery levels- although it's easy enough to remember (more blinks is good), counting out 6 slow blinks could be annoying, but make it blink too fast and you could miss the number....
==It's fast, but clear enough, we will try to publish a video about it.
Apart from that, seems a really good UI. Can you do the ring with just a thumb?
==Yes, I always do so. And other finger around the waist. And two fingers to control the ring is also very natural.