I would say one of the biggest benefits to an open top other than allowing better light is allowing proper gas exchange. As oxygen is dissolved into the water, carbon dioxide and other gases is released.

Glass top all the way, even my sump is covered. Way less evaporation, nothing can jump and nothing can fall in. With adequate water movement gas exchange is not an issue. As for heat, well the house has central air so no issue there. Another plus is the lights don't get any salt creep or water spots on them, so the lights last longer and with the lights staying in brand new condition it makes up for the light that the glass blocks.

this and this might help.

Actually very good points

i removed my glass top about a month ago. I have a custom led setup built into my canopy. I am now worried my wiring and leds well corrode as my leds are open and about 6" above water surface, would any suggestions?