It depends on the temperature of the room that the cage is in. A single heat lamp might be enough to generate the hot side and keep the cool side in the proper temperature ranges, but if the room is on the colder side a 100 watt bulb on the hot and a 50-75 watt bulb on the cool side (both hooked up to lamp dimmers. see link below) would be ideal.
Lamp dimmer: http://m.homedepot.com/p/Lutron-Cred...ite/100145680/
The thermometers are usually by the lightbulbs.