Eugene, good to hear about the NiMH. Re requirements: I took the initial post as a challenge to meet certain specifications. 1) total weight under 1 ounce with everything, 2) super compact when packed (Doug even said the tiny e+LITE was bulky), 3) powered by replaceable, non-rechargeable lithium cells for shelf life (and I'd add cold weather performance). And I'd add mechanical switching to eliminate parasitic drain affecting the shelf life. But that is all somewhat artificial, aimed at an emergency kit light intended to sit unused for years, not that common a plan.

Ultralight hikers are fond of the Nitecore NU20 which is quite bright, is USB rechargeable, and weighs ~ 1 ounce including battery but not including their somewhat overweight headstrap which is another ounce. Some people replace the headstrap with one made of shock cord (see imgur pic above), that weighs just a few grams. The Petzl Bindi (36g including headband) is comparable and I might prefer it to the Nitecore if I were shopping for this type light. Either gets the weight to a little above 1 oz, but both miss on the non-rechargeable lithium requirement. I'd still call them good ultralight answers even if they don't quite meet Doug's spec.

If I get a serious headlamp myself, it will probably be 18650 powered rather than ultralight. For now I'm ok without one since I don't go caving or do any other hardcore headlamp things.