I would say as far as visible light depends on the quality of the bulb.

Op you said you use uth so what I would do is take the temp of the cool side without any lights or che and if it stays around or above 78 then I wouldn't use the light but if your cool side is lower than that I would place the domes over the cool side and dim them to keep them around 80. I personally don't use them as far as heat or viewing but I do use non visible reptile lights when feeding bc the room is very dark and it gives me the ability to see without disturbing them, I'll use them to check on them during the night or if I spot a mess also.

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