Bryan, if you find that it blocks any light or it gives you a grid pattern underwater with the lights on, I have a suggestion for a cool compromise. Bulk Reef Supply sells DIY mesh screen kits. The mesh they sell with it is actually clear, and the spaces are 1/4". These let all the light through, provide adequate air contact, keep even the smallest fish from jumping out, and are also quite visually pleasing from the outside. I have a picture or two of the one on my tank in my tank build thread. You just cut it to size and install the mesh, and you're good to go! Food for thought, anyway.
Good luck on the leak testing! I hope it all turns out well!