If you use a rheostat or light dimmer switch, you need to have a thermometer probe to monitor the temp, then you make adjustments to your rheostat to bump the power up or down to your heater. if you are getting a thermostat, you will want to get one made for reptile cages, not a room thermostat at the hardware store. you will need also a thermometer probe with the thermostat (i believe they all come with a probe) so that it knows when to turn on and off. cheap thermostats work by turning the heater on and off to keep the temp correct. good thermostats are proportional, meaning they work by adjusting the amount of power sent to the heat pad until the perfect temp is achieved, keeping the temp constant and steady, rather than turning the heater on and off as the temp gets too high or low. a rheostat essentially does the same thing, adjusting the power flow to the heater, and is less expensive. the downfall is you can't just program the rheostat to a specific temperature - you have to use a thermometer to monitor the temp and adjust the rheostat until you find the right power setting.