I had two 13 watt Exo Terra bulbs in one of the compact tops on my viv... then I turned them on. They're insanely bright, and almost painful to look at. Ajja was less than pleased. Those bulbs are now sitting in the boxes under my stand. Instead, I use four 15 watt heat bulbs in an Exo Terra compact top. The daylight bulbs are on a timer and the moonlight bulbs are on a thermostat. Temps stay very stable, and using a few very low wattage lamps seems to have less effect on the humidity than one scorcher.