PAR and WPG
It seems to me there is a problem with using watts-per-gallon (WPG) as a particularly effective way to determine how much light one has. I have been reading and thinking about this, and I am unclear on this aspect.
For example, if I have a 10 gallon All-Glass aquarium (20x10x12 in) and an AH Supply 36W Bright Kit with their wood hood. The hood places the light approximately 2 inches over the water, or perhaps glass tank cover. Using WPG, that gives ~3.6 wpg. Pretty high light. I think, however, it is not very even light coverage, however (meaning a PAR meter would not show the same value front-to-back, or side-to-side).
Would not raising the height of the light over the tank eventually get to a point where the PAR values would be much more even and better(?) for the tank?
Obviously, as physics goes, the PAR value would lower. I am not thinking this is a bad thing, per se. As other articles and postings on here have proposed and shown, that lower light is not a bad thing, that 1.5 WPG can be used to grow nice, healthy planted tanks. (Just slowly, in a more controllable manner.)
That said, what are “good” PAR values? What would 1.5 WPG be roughly equivalent to in PAR? And 2, 3, ... WPG?
I realize this message is a little but jumbled, logically, but then so is my thinking and understanding of the material. I could use a little help in sorting out the details.