Beautiful tank!
I am thinking about having one built with similar dimensions, but not a full cube. Something like 36x28x24(tall). I have planned for the spectra as well. (Not planning to add LEDs)
My main concern is this. I really want to limit the light spill outside the tank. At the same time though, I would like to get as much coverage as possible.
In your case, with the perfect square dimensions, I assume the problem is to get coverage front to back while at the same time not getting light spills to the sides of the tank(?)
My above dimensions are by no means final. They are just a rough estimate at this point.
Given your experience with the spectra, what would you consider ideal tank dimensions in order to get maximum coverage + minimal spill?