This is a design for a piece that fits over the lamp in the lid of a 30 liter BiOrb fish tank (probably fits on other BiOrb tanks too).

I made it to make the tank slightly less bright hoping that helps stint the growth of the algae somewhat, and it looks nicer too!

For more information about the project go to: http://www.macouno.com/2012/09/14/creating-a-cut-out-for-the-biorb/