actinic lighting

[StirCrazy]

while we are on lights .. something has bothered me about the way people figure out there light.. everyone says to get to so many watt/gal but I feel watt/square foot would be a better estamation .. am I out to lunch or what?
the way I see it with 312 watt of light (after I get my actinics) I will have 6.24watt/gal in a 50 gal tank.. but measured the other way I would have 69.3 watt/ square foot, I am interested to hear what other people have /square foot.

Steve