It depends. My lamps are about a foot from the basking spot. I had to move the set up to another room when I got the UV light, because it only plugs into three prong outlets, and the 100 watt flood was just not heating up nearly enough, I started switching around until I ended up with my current, which is a 75 watt nightbulb in one lamp, and a 60 normal in the other. Note that I had those thermometer problems with all the variations I tried.