Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Window screen cuts out light, too. Not sure how much.
It is used when you want the air flow of an open top, but have fish that jump. It offers no protection at all to the light fixture. Splashes can go right through it and invade the electrical parts of the light (depending on the details of the fixture, of course!)
You can make your own window screen from parts available in most hardware stores, and test it out. Once you have made the frame you can try any of several materials as the fabric part. To find different grades of netting look in fabric stores and garden stores.
In garden stores there is a black mesh sold for protecting fruit trees from birds. The mesh is about 1" x 1". In fabric stores you will probably be looking at material sold as Tulle. Either of these are filmy enough to allow most of the light through. I am very leery about the garden store material. I used it over a pond to keep out raccoons. The raccoons went through it anyway, and the mesh ended up in the pond where it caught several fish. Between the mesh and the raccoons I lost a lot of fish. :-(