I know and support what you say, but I can't get why you say "PPFD also changes throughout the day"?
PPFD is a cumulative value - all the light which plant get per day. May be you have been in a hurry and mean PPFD is not the same every day?
But we talk anout tanks, not lakes.

As for w/gal/day rule - this is forces aquarist to remember about PPF per day (it's a good sign
Without this folks often say "I use low light - 1wpg", while their plants get the same amount of energy for growth as his nabour's with 2wpg.
This is "why" I say it is a little bit better than wpg rule.

To be fair, W/gal/day is a good "quick rule of thumb" to estimate what you have without mesurements, but we must not forget the type of lamps and reflectors and other factors you mentioned. We can't measure everithing and everytime... and don't need that to grow lush plants after all.

You are just right, we can't take it as a precise rule.
Many folks know that, I hope, so I simply do not see any need in posting everytime all that factors you mentioned in last post so I omit 'em.

Will you do the patterns like ADA's?
Will you try to do the same with Super-Spreader® ?
I think we can have some use from this device.


naman