Thanks!

I must have read about this upgrade on a flashlight site, for bulbs with a flange base; you're right of course about the optical requirements.

This lamp essentially radiates into a nearly perfect hemisphere. Some focusing occurs due to a reflector and some lens shaping, but the beam is not very tight. I was hoping I could just get some more lumens out of it.

I'll have to see about an LED upgrade, with a rectifier, possibly a doubler. I do have 6 volts and 3 watts to play with, even from this old generator.