The Mat Stat is an on/ off switching device, that can be used with a variety of heaters. It has a new accurate dial calibrated in both Farenheit and Celcius. Ideal for controlling heat mats, and other low powered heaters up to a maximum load of 100 watts. Now with both Heat and Power indicators. The power indicator will shine whenever power is applied to the unit and the heat indicator will shine whenever power is being supplied to the heater. Namely, when the heater is on. This thermostat is not suitable for controlling light bulbs. The constant turning on and off of the light bulb would not only distress your animals, but would cause frequent failure of the lamps. This, in turn, is very likely to make your thermostat fail. The Mat Stat, alongside the temperature themostat is one of the best selling thermostats in Europe.