My tank has 2x t8 tubes. A daylight and a powerglo. Its at 55cm high tank, no CO2 and some root balls in the gravel. My xmas moss grow great in there, glosso also grows pretty good, but it keeps getting covered by my other plants so loses the light all the time. In your shallow tank you should have too many issues with light id say. With light, if you double the distance you get a quarter of the brightness i beleive. So essentially you would have about 4x the light of my tank... But feel free to prove me wrong