I have not used Vision much but I would be very surprised if you would be able to do this directly. It should be straight forward to get an average intensity with or without Vision (convert image to 2D matrix and average the values, for instance) -- the difficulty will be correlating the calculated values back to Lumens, etc. This could likely be done but it would probably require you to come up with the calibration curve and would be sensitive to setup changes, dust on the lens, equipment aging, etc. and these things should not be discounted. This is why, particularly if you're in a production environment, you'd probably better off buying a commercial meter and talking to it via a driver than to try to do it yourself -- they've already taken these things into account.
One more thing, in the picture you attached, any luminosity calculations you made would probably be skewed low as the white is saturated (railed) in spots and those under-reported values would affect your average. If you did try to come up with a Lumen calculation, you would probably want to turn your aperature and/or exposure down before creating the calibration curve.
