Welcome to the never-ending journey of understanding reef aquarium lighting. I've been studying this aspect since the mid-90's and I now know less than when I started.I am new to the lighting aspect of reefing, but I am diving head into it to learn.
The seneye and laptop setup my friend brought over to map my tank had 2 readings...
1 was PAR, Potential Available Radiation
The 2nd was PUR. Usable radiation.
He knows more than me, but from what I gathered in his explanation you are aiming for 70% PUR. It relates in a sort of telling u how much of the lumens detected are usable in the photosynthetic spectrum... or something along those lines
Again, I'm learning still. I will know more as I skim @Dana Riddle 's articles.