Hi Hoppy. I'm new here. Have you measured the PAR using 30" tanks like the 20Long, 29g and 37g? Most bulbs, PC, T5HO, T8 and T12, are approximately 22" long. This configuration has approximately 4" of space on each side that is not directly under the bulb. (I know that Coralife has some 30" T5NO and T5HO fixtures with 28" bulbs available and Zoo-Med
has some 30" T5HO fixtures with 28" bulbs as well. We can use your presently available charts to find the PAR for these fixtures.) I am interested in the 22" bulbs over 30" tanks because so many people have this size of aquarium. You could probably extrapolate this reading of PAR.
One more question concerns your PAR measurements in the graph showing the distance from front to back. Why are there 10 micromoles difference at 4" from center in the aquarium with no water and the tank with water has 5 micromoles difference. Why is there a difference when measured from front to back? The back side of the aquarium has more PAR than the front side, if I am reading the chart correctly. Why is this? (I am not concerned with the 5 micromoles difference from an aquarium with water in it and one without water.) Why does the PAR increase on the back side verses the front side? It would seem to me that the front side and back side would have similar readings as the distance from center increases.
One last question. Why do the aquariums with water in them have a higher PAR than aquariums without water? I would guess that it would be the other way around. Aquariums without water would have a higher PAR reading that aquariums with 5" of water in them would be my guess.