For fluorescents to produce any significant UVB they require a specialty mix of phosphors. I'm not aware of anyone that makes a UVB producing T5 bulb, though it would be nice! T5 bulbs in good reflectors would be great for providing good lighting to your plants (and good lighting has psychological benefits for many animals, perhaps including chameleons) but for UVB, T5's won't work--you'll need either a fluorescent or mercury vapor bulb for that.
cj
p.s. UV light is non-visible to our eyes. Two bulbs could be throwing off wildly different amounts of UV and look exactly the same to our eyes.