Michael Goode , Jan 02, 2001; 11:39 p.m.
well, I can't completely help you, but my Minolta Auto Meter IV manual has a formula for calculating lux from Exposure Value, and the formula is lux = 2.5 x 2 ^(EV). I just measured the light in this room, and I got, at ISO 100, F2.8 at 1/30 sec, at EV8.0. So the lux value would be 640. Using your formula, I would get shutter speed = 1/(640*.0929). So shutter speed = 1/10 second using your formula, whereas the actual meter reading, if I had used an f-stop of root(ISO), would be f11 at 1/2 second. In which case, your rule would underexpose the negative by 5 stops, which is, um . . . bad.
Looks like your formula needs some work. I am too tired to do some serious mathematical derivations now, and don't think I could manage it anyway, so I'll leave it up to you to improve the formula.