With the heat light (red bulb, until we get a blue bulb), the room temperature is a noticeable 78* (by the door where it is influenced from cooler air coming in from the hall, snake bins are about as far from the door as they can get, so probably warmer). The thermometer inside is now reading 83/86, humidity still holding. So I think I've got it! The light is currently suspended about 4 feet above the bins. I'm going to lower it so it's closer and more localized on the hot area. Hopefully that will succeed in getting the hot side just a little higher and make a better gradient.