I use a lamp or two depending on tank size, all hooked up to thermostats. Leaving a light on all day will definitely zap all the humidity quick. My room sits at 75f. Thermostats are set to 80 to 82 depending on location in the room. They come on for a 5-10 minutes a hour basically. Tanks are insulated with foam board. Humidity never gets lower than 50. But I usually spray every 3 or 4 days to keep it higher.

After I insulated my tanks I found my uth did bring the ambient up a few degrees. I also use bigger uth then the size recommendation. And they actually go about 2/3 across the bottom lengthwise. Ending a 4-5 inches before cool hide but still completely under water dish. But just having your lights controlled by a thermostat they will only be on when you need them and not killing humidity constantly.