Ok got you. My first main tank had glass panels/sliders and I'd say they helped keep evaporation levels down, acting as a condensation tray and stopped fish jumping although I did have another lid on top. The light was never exposed to the water in any way.
Cons of this tank were that algae grew on the under side of the glass over time so needed regular cleaning and also lime scale built up but that was due to the hard water down here. Plus there was limited access to the tank, at least on the one I had as the glass panels were smallish.
As they algae/lime scale grew light levels dropped.
I have to say my current tank has no condensation tray and the lights often get lime scale build ups on them.