Its like a ceramic heat emitter Methinks. Expensive but longlasting. I use low wattage heat mats (30x30cm) in my 4x2x1.5 and a fluro tube for light. The Thermostate still clicks them off as they get too warm. This is brissie climate I am talking about. In a 3ft tank that is 50 cm high I have a 40W bulb running and the thermostat set at about 33C and is still clicking off.
For summer you wont need much wattage at all, Winter I use 75 to 100W bulbs.