I think if a guy had a light with a dimmer switch he could adjust it up and down and use the meter on the camera to see what the exposure is. Set ISO at 100, aperture wide open and monitor with shutter speed.

Another thought is, if you had ND filters you might be able to cheat the light down using different combinations.

I am sure there are formulas but I am not sure you would need it for this real world test.