I've always wondered why headlamp mfgrs don't grok the need for 4- and 8-hour duration. Just gimme your best for 4 or 8 hours. That's what's asked of me, and that's what I ask of my light.
BTW: 37 lumen for 10 hours is what the H60w put out on an 18650. Would be amazing to see that in a 1xAA format.