We had difficulties when trying to get repeatable PAR readings with those 8.5 inch diameter reflectors with CFL bulbs. There are just too many variables, including the actual physical size of the bulbs, which varies with manufacturer. I keep thinking I will go back and work on this again, but I haven't done so. I can't figure out a way to get data that will work for a variety of reflectors, bulbs, manufacturers, etc. I hope someone else will work on this.