The Ceramic heat emitters are awesome, but on a 20g converted to vertical you wont want to use them. The heat can and will crack the glass on the top of the tank. Now if your converted 20L has a screen in the top section above the door than you could mount the CHE so it is pointing at that and radiate heat into the tank through the screen.

I never liked using any nightime lights with nocturnal frogs. My Reds all ways seemed to be bothered by the red glow.