I currently use a mercury vapor lamp for my RES. However, it has to be at least 18 inches away, and when I keep it that far away my basking area doesn't get warm enough. I've heard basking temps should be 90-95 degrees, or that they just need to be 10 degrees warmer at least than the water temperature (which is currently about 70). Which is correct?
Also, is it okay for my water to be cooler in the winter? it varies from 70-72 right now, 75ish in the summer. Basking right now varies from 75-82 (it's usually higher but we literally don't have heat in my house right now, I'm heating my bedroom with a space heater).