One 123 or a Lithium AA, Naaa. No run time for the light output. I don't see the sense in it...........
You are going to have to have 3 AA Mah capacity to have an acceptable light. The SL one watt is long, yes, but stick it in your belt.
This is not going to be a ARC sized key chain light with a one watt , period, unless someone comes up with a AA or AAA with the Mah of a D or C cell. Won't happen for a long time.