lighting on top of acrylic tanks

[Mmorse]

I am going to make a custom hood for my acrylic tank and was wondering how you all would do it? I was thinking of buliding a piece of plexiglass into the hood so that water dosent evaporate into and ruin the lighting. But do you think this would greatly lessen the light penetration because the light has to not only go through the plexiglass but the top of the acrylic tank? I will be running 2x55 pc's plus a 18" flourescent atinic tube