Resistored LGI for use with AA lithiums?

A part of me considers this blasphemous, but still I can't shake the idea of adding a resistor to my LGI so I can use AA lithium cells without burning up the (already well overdriven) Luxeon. The lithium cells would do two good things, namely maintain light output in cold weather and run at near-full brightness over most of the battery's life rather than fading gradually. But what value of resistor to use to protect the LED yet not cause it to dim, er, at all?

Also, is there such a thing as a resistor "coin" that I could simply drop in ahead of the batteries, or perhaps between the last battery and the tailcap spring?

Why don't you first check to see how low the Vf is on your LGI. Try it with two lithiums and a dummy.

I have a Q2H that Lambda put into a Brinkmann 2AA as a Direct Drive "Lambda Safety Illuminator" that is considerably brighter on 2 lithiums than my more recently purchased BadBoy 400 Q3L. The LSI also runs for much longer.

Admittedly, the LSI is not as bright as my two LGI's on either 3 alkalines or 3 NiMH's. My LGI's both appear to have a pretty high Vf. This is supported by the fact that these LGI's seem to run brighter on alkalines than they do with NiMH's. After 45 minutes on NiMH's, they dim considerably.