If your cage is indoors I recommend two lights. One to provide light and heat. A second to provide the appropriate UV rays that your chameleon will need to grow properly.
Providing heat can be accomplished with a simple and classic incandescent bulb - the type we use or previously used indoors.
Proving proper UV-B for a panther can be accomplished with various bulb types. Most people recommend the Reptisun 5.0 linear tube.
You can get more info by searching the forums.