When you think of what egg crate is normally meant for (light diffuser), it makes sense that it would reduce/scatter the light entering your tank.
It won't really affect anything directly under the bulbs, by the further away you get from them laterally, the more light they absorb. On my last tank I had a hybrid glass/egg crate cover, where the glass strips were right under the bulbs, with egg crate in front and behind. It worked great until I found out those thin strips of egg crate weren't heavy enough to stop a full grown labouti wrasse leaping at full power.
|