There are inexpensive, good, fully regulated buck drivers like the LD-29, or check here if in the USA for other options. No pulse width modulation crap and constant brightness on all modes independently of battery SoC (State of Charge).
At last and not really wanting to start a :-D fire, XM-L2 U2 emitters? Typical cool white low CRI stuff? :facepalm: In the darkness of a cave I think it is of primordial importance to have light of the highest quality. High CRI emitters of low to moderate (warm - neutral, 3000K - 4500K) temperature. Your more or less darkness adapted eyes will enormously thank the light temperature and color rendition to appreciate the details of your surroundings. Some CRI90+ candidates: Samsung LH351B 3000K and LH351D 4000K in this thread from AEDe (CRI90+ LH351D 4000K here in MTN Electronics too), CRI95+ Luminus SST-20 3000K & 4000K, Nichia 219C (various offerings in MTN Electronics too), and of course Clemence's shop, high CRI paradise.
Cheers :-)
Mon, 10/22/2018 - 03:34/06:17