It depends on what the temps are in your home, what type of chameleon you have, and how you have your basking light set up. The best way to figure it out, is to set it up and carefully monitor the temps to see if it's what you need. I use digital thermometers and a temp gun to check the temps in my cages. I have one probe at the basking spot and another lower in the cage to see what the ambient temp is doing.
I have several different wattages, and change them to higher or lower wattage as needed. Except on the cage that I have a dimmer switch on the basking light. That one, I use a 100 watt bulb, and just adjust it with the dimmer.