Okay... good point. A standard is good. I can use your method to verify a single EV between my handheld light meter and my DSLR's metering at any given time outside in daylight... I'm pretty sure they are within a stop of each other, and I can zero out my hand held to match my DSLR's metering, as the DSLR is most likely spot on. So, assuming that the accuracy of my DSLR is adequate, I would simply need to use a bulb that is bright enough at full power to meet or exceed an EV of 15, and then by reducing voltage, I would reduce luminescence... as my light meter reads a full drop in EV, I would simply mark that position of the dimer switch with that EV... and then re-test to verify... in theory anyway. Should I be worried about color temperatures? I would think just how bright and what my meter says the exposure is for shutter, aperture, at a given ASA/ISO and look up EV on a chart (work backwards really from EV desired, until I get shutter and aperture the same on my DSLR)... I'm just not sure a projector bulb will respond well to having a dimmer switch in series???