I didn't comprehend everything about the SolarForce product line either. The SolarForce light I'm building up is something of a project and a toy, although it will undoubtedly be a very bright light. When I ordered the K3 head I also ordered the extension tube so the light would have two 18650 batteries. Thing is, what to do with the L2P head? Then I saw a SolarForce two battery L2 tube and a tailcap that would be more suitable for a larger/longer light.

Bottom line, by the time this build is complete I'll have a three battery L2P tube (two battery main tube pls extensio) with the K3 head, and enough extra parts (the original L2P body) to build a straight-up 1x18650 L2P with a SolarForce 3 mode LED module. Both should be good lights (assuming all the parts play together) -- one a 1500 lumen flamethrower and the second a fairly normal 320/128/32 lumen output light -- 30 hours of runtime at the low setting. SolarForce 320 lumen 3 mode .8-4.2volt bulb

Interesting, but the only review of the bulb complained that it didn't fit correctly (too long) in a Surefire 6P. LOL. I had just the opposite problem with a 6P bulb being too short for the L2P (hence the beginning of this project). The bulb I originally bought fit perfectly in my SF 6P and that is now a great light, albeit CR123A only.

Parts is parts.