If you mean a glass top to prevent water splashing on it, that would be one thing. To cut down on the light penetration, I don't think you'll need a top for that. I have a 48" over a 33L shrimp tank, and it's great. As for splashing water, it's already water resistant, so you're probably fine there as well unless you have water movement that is splashing right on it. That happened to me on another shrimp tank that had a sponge filter. I just moved the sponge filter to take it out of the way of the light.