If you're lucky, the lamp or solar spectrum and the sensitivity spectrum of your emulsion will be fairly flat around the peak sensitivity of your meter. In that case, you'll be able to do test strips and get reproducible results.
I'd begin with a step-wedge kind of approach using a reproducible (lamp) spectrum. It seems that with a little upfront work, you iwll have a very handy device!
I am a bit more skeptical about using it for the sun exposures- the spectrum we see observe here on Earth changes a lot with the weather (UV scatters a lot in the atmosphere) and has a big slope in the UV:
But at least you should be able to get ballpark exposure estimates.