hoppycalif· Premium Member
Glass tops do collect condensation, in my experience, so they do attenuate the light at least a little bit. What I used to see is a glass that was just dripping with water every morning, but the water evaporated soon after the lights came on. That means a residue of crud on the glass which also attenuates the light. I got tired of trying to get rid of the crud, so both of my tanks are now open to the light fixture. The condensation I get inside the light fixtures has not yet caused a problem for me.