That's not possible with lamps in the corner
The problem, as I am sure you are aware, are the corner blocks. Take a look at a two high section:
To light up the corner blocks, we need to power an adjacent lamp directly, by pointing either a repeater/comparator, a line of redstone dust, or a torch (from below!) into it. Simply powering the adjacent lamps (such as by placing a redstone block/torch next to them) won't do. We can't do that directly on the corner blocks, meaning we have to power either both green or both red blocks directly.
However, none of the methods capable of directly powering a block fits in a 1 high space. Nor are there ways to directly power two blocks on top of each other at once, making a 5 by 6 full cube impossible.
Solution without corner blocks
However, if you leave out the corner blocks, it's definitely doable, although a bit of space below will probably be needed. The corners are still tricky, but you can use a torch/block/dust tower to light up most of it. The torch is connected to the input (green) underground.
Click on the images to enlarge them.