The only way to know for sure is to have a proper humidity gauge in your cage.
More frequent mistings may be necessary. Also adding live plants to your cage will help give it a humidity boost.
If you want to go with a double fixture, you should definately go with a t5ho. Put one Arcadia 6% UVB and a 6500k day light bulb and your plants and your Chameleon will be VERY happy!
T5s are just so much more energy efficient and the amount of light they put off is so much greater than that...