sbslider
(sbslider)
11
I have a recommendation that does not meet your criteria, but I share it anyway. Thrunite Ti-3. I used this light with a lithium primary 3 weeks last September. We did not night hike. We did live away from most civilized contact for those 3 weeks. John Muir Trail, only supplies available on trail were at Red’s Meadow and Muir Trail ranch. I had mailed a spare AAA lithium cell to Muir Trail ranch, and did not use it. It was clipped to the brim of my visor and provided light where I needed it. I rarely used anything but firefly mode. BTW, I’m 56 years old and my eyes are not the greatest. You just don’t really need a lot of additional light in the back country. Advertised at 0.04 lumen, 12 lumen, and 120 lumen. mode order L-M-H. Actually not far off from your medium level of 20 lumens, likely could not notice the different betweeen 12 and 20, and run time at 12 lumens is 6.3 hrs. 115 hrs on firefly.
That said, if you really want something more “survival”, I would agree with those that suggested an AA battery instead. 3x the capacity with little weight penalty. No specific recommendation for an AA light though.