I was having the same problem. I cut a piece of cardboard to fit my screen top with a hole big enough for my light and some ventilation, then wrapped it in aluminum foil It helped a lot for ambient temp as well as humidity. I also switched to a red bulb that is on a dimmer switch for room temp fluctuation. Made a huge improvement. I just set it on top of the screen and it is held in place by the screen locks.
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