Like blackcrystal said, if the room temperature changes, then you need to re-adjust your dimmer switch, as it's only a temporary fix. You need a good thermostat to keep the temperatures. I use a dimmer switch perminately but, I also have them in my room, and I know what to adjust them at what time so it stays at the proper temperature. One snake tank I keep in the 85-87 range(warm side) during the day, while the other stays in the 87-90 range. Night time my temperatures drop to 80-81 range(warm side) and 82-83(warm side).