> I am trying to substitute the flash units I use with studio lights of equal > or higher luminosity. The guide number doesn't give me an idea of how much > lighting the flash unit provides in terms of luminosity when compared to a > standard lighting fixture used for studio lighting. Studio lights are > usually sold and measured in terms of either Watts or Lumens and I need to > find out how the different flash units I usually use compare to this lights. Joseph Does your ambient lightmeter also have a FlashMeter? If so do a quick empiracle test, assuming you can get access to studio lights and possibly a studio flash of known power (Joules) output. Take an ambient reading with the lights on a known setting (full) Take a flash reading with a studio flash on full at a measured distance You have enough info there to create your own conversions. As Karl stated: guide-number to power depends on a lot of things, not the least of which is reflector design. Next is understanding the difference between quantitative measurements of "light" and those of radiant energy. Two units could consume equal power (watts) yet produce wildly different amount of visible LIGHT. The fraction of energy emitted as UV/IR instead of light for instance. Reflector design of course means that in one case the light emitted could go in all directions, in another be in a highly focussed collimated beam. Bob
