What wattage is the UVB bulb? I would recommend either a ReptiSun 5.0 or Arcadia 6% bulb, preferably a T8 or T5 tube, although the CFL versions can also work if set up properly. If you have to stick with an Exo-Terra CFL, I would recommend a 26W UVB100.
Whatever bulb you use you need to provide basking spots at different height from the bulb so your chameleon can regulate his UVB intake.