I found this link to calculate light need here
. Anybody else use it?
I think it's as useless as the prior post suggest here in this thread.
It does not measure what the plant's are receiving, you need a meter to measure that and to fairly compare light from one tank to another.
It's a good attempt however. But nothing beats measuring the plants and in the tank in question.
This also gets around brand names, reflectors, smugdes on glas,s lids or not, differing plant heights, corners, uneven lighting(bright in some places, not so bright in others) etc.........
PAR meters are relative cost effective and the data is more useful.
You may share or perhaps even rent one from another member etc, then adjust the light to where you want it.
Apogee makes a cheaper version and they are about as good as LiCOR's.
A few clubs bought one to share amongst their membership(not a bad way to go).
I honestly have never had issues with the W/gal rules, but the light has become more efficient so I've gone to lower and lower light watts over the years.
So what was once 2-3 W/gal, might be 1 or 1.5w/gal today.
A meter gets around that issue also.