I prefer throwy headlamps, because they can be run at a lower wattage, with 10 hour runtime at the highest possible lux and lumens. My goal is now 1000 lux at 2 meters, with the best possible efficient in the driver, heat sink, led choice a 2s18650 is a good choice for a worklight, and I have not fully explored a 2s21700, although I have been using one for the past 6 months. I have have been using 2s18650 for the past 10 years, and often forget I have it on.
I personally don't like the compromise of output going to a 90 cri. And I do not like going below 4000K, and dislike yellow lighting. 4k is as yellow as I go. I like the spec tradeoff of the 80 cri leds.
I have been using 4k 70 cri leds for color inspection since late 2015. But I also like the color rendering of a cer 5300 Kelvin xpg. I only own one 90 cri light which I rejected on the basis of the shorter runtime because it needed more juice to see well, as the led was not as efficient as the xpl v6 that I normally use.... I personally, do not go for any headlamp without at least a 32mm aluminum reflector. And ar glass lens, 92 percent efficient buck driver, cpu finned heat sink, and infinite dial dimming. The controller needs to distant from the led, so it can be heat sinked separately and not cooked by the excess led heat. Of course, I make my own. But haven't since 2016, and waiting for some improvement on led efficiency or battery, which has not happened in the past 7 years.
I have 2 xph series emitter headlamps. The Chinese one is garbage, even with a zoomy. The Fenix is a good light, but rather bulky and the runtime is about 67 percent what I need. I am constantly fiddling with the output and often make mistakes. It is far better to just make a light as efficient as possible with as large as possible battery system and make the light have a minimum of 10 hours runtime. And a dial to get runtime as long as 300 hours. With a good setup it could be bright as 7500 lux, 450 lumens, and a minimum runtime of 10 hours. I wish I didn't have to spend days shopping for parts from 12 suppliers, and a good half day assembling because light makers make sub par lights. Apology to those who get close.
As far as a single cell goes. The best thing I ever own was 3 imalent hl25 lights with a dial and xplhi. The light made a half way bright enough worklight for 3.5 hours of runtime, which is way better than a flood zebra walk in the woods light. But 3. 5 hours is not very long, and they were not very durable in my opinion, at least for a belt loop edc. I do have one of the three 2017 that still works and I am wearing it now, although I have been using the $250 Fenix xhp50 2s217000 all day..
My next homemade light might use a buck Puck 1000, with dimmer, a 32 to 36 mm aluminum reflector, the highest bin 5000k xpg or xpl possible, a cpu heats sink for the led heat sink, an avid heat sink for the open air bezel, AR glass, a copper refrigerator tube for the pivot and additional heat sinking. A plate and homemade band, maybe 2s21700, and lots of thermal epoxy, usually jb weld with zinc dust mixed in. The switch is always the failure point weakness in my home made lights, and I have need of replacing them every few years. The wires from the rear to the front also need to be fixed every few years. And the lithium ion batteries need to be replaced every 3 or 4 years. I have always used protected Panasonics. I tried unprotected 2 years ago, but seeing a shorter lifespan on the unprotected. I just got frustrated with tripped protection circuits and the difficulty of resetting. I am still waiting for a better technology than lithium ion. I passed out years ago holding my breath.
