How far is the basking branch from the lamp and how old and what type of chameleon is it? 6% might be better if the lamp is close to the basking spot and the animal is young and still climbing on the top of the cage. If it is an adult, and you have say 8-10" between basking spot and the lamp, you are fine. Even with a young chameleon you can just raise the light up higher and lower it a little each month as the lamp wares out and UV is less intense.