Your are basically correct. Are you growing surface plants or are you
asking if the available light at the surface of the gravel will be the same?
The lumens will be less at the surface of the gravel on a deeper tank.

DJay


"Dan Norgard" wrote in message
...
It would seem to me that the depth of the tank would be the determining
factor in lumens, not the gallons. ie: a 24 inch deep tank would require
more light than an 18 inch deep tank even though both were 40 gallons.
Anyone agree or am I all wet? Excuse the drawing...
OO
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Dan