Best LED for low/medium current?

So I’m going to start looking for driver and led for a low-medium output P60 build to run off 2AA or vampire a single cr123. Drivers are few and far between but there are a few on the import sites I plan to try. What LED would be best? Not sure what modes I’ll end up with but in a perfect world I’d like 2-4 modes ranging 1/2 lumen to around 100lm max. I’m strongly biased towards high cri in the 3500-4500k cct but could compromise a little on cri and/or tint for the right emitter.

What would be the most efficient emitter in this range? We’ve made big gains at big current but does anything clearly beat the cheap and widely available xpg2 in a warmer tint? Any thoughts on the high cri xml2? Where can they be sourced?

What does “most effective” mean in this context? A Samsung LH351D would be efficient, and comes in 4000K, 90 CRI.

I don’t have any specific LED recommendations for you. But the best thing to do, in general, is look for the LED with the lowest Vf that will at least reach 100lm, and has good efficiency at that level. The low Vf will mean that you can run the batteries down as low as possible while staying in regulation.

For CREE brand emitters, there’s a handy online comparison tool called the CREE Product Comparison Tool or PCT for short. I wish other manufacturers had such a resource. I use it all the time. I don’t know how to tell you what it is or how it works. You’ve got to see it for yourself. But basically, they have almost all of their emitters in a drop-down list, and you can choose up to three of them at a time to compare the properties.