Hi Clare,
I use one Repti-glo 2.0 bulb with helps with the live plants and generates almost no heat. I then use a 2nd bulb at 15 watts to get my temps to about 80 degrees in the day if needed. Since my home temps are at 68 - 70 at night the unit needs no heat.
The 2ND bulb can be a red night time bulb or black light so you can add some heat at night if needed or just to add some light for night time viewing.
I find that most of the time I can just get away with only the 2.0 bulb on since the sun heats my room to a nice 75 - 80 in the day.
I keep Red Eye Tree Frogs in this setup.
Don