Okay... so I like to ride my horse at night. I modded few headlights in past, and found that I sometimes like to use _very_ low power levels. Like 10uW (That's 0.001 lumen IIRC), because they preserve night vision, don't annoy people around me too badly. I even put a headlamp on a horse... it worked, but then I realized that it may not be so good idea. Now... my girlfried gave me Petzl Nao (big thanks to her). It is beatiful, feedback-control is actually very nice. But... it does not really have low power modes, and does not fit under helmet. My horse says I need to wear a helmet (6yr old fjord). I tried setting it up on the computer (and control software is slow with bad user agreements), but even lowest setting is way too high -- and that would not help with helmet issue, anyway. So I'm getting something new, Zebralight H600F should be on its way, 700lumen max and 0.1 min.
Nao low-battery behaviour leaves something to be desired. You have light on lowest setting to preserve power, and then got hit by three unexpected, very bright flashes. I did not like that, and nor did the horse. Ouch and when battery goes _really_ low, it still shines (good), but can't be turned off (odd).
And a bonus horse in Berlin's subway story.