If you worried about skin burns, there is a simple test. Put you hand under the light, where your chameleon basks, and keep it there. If your hand feels not just warm, but begins to feel uncomfortably hot -- begins to feel like it is burning and was impulse is to pull your hand away rather then leave it there -- then your chameleon's skin will burn under the light.
Even with a relatively low wattage incandescent bulb, some reflectors will focus the light into one intense hot spot. Whenever I use either a light with a reflector behind it or an intense bulb, like a halogen bulb, I test the overall temp and check for hot spots with my hand. This doesn't replace using a thermometer, but it will tell you whether your light could burn your chameleon.