Now, I'm a firm believer in housing all chameleons in all screen or at least 2 sided screened enclosures. BUT!!!
Here is what "World renowned best selling author on reptile care and husbandry" says in his book: "Essential Care Of Chameleons":
GLASS ENCLOSURES WITH SCREEN TOPS
Although some have made an issue of the suitability of glass walled enclosures with screen tops for chameleons, this thinking is incorrect. Certain species require high relative humidity and do well in large all glass screen top enclosures. The reduced ventalation helps maintain an optimal level of humidity. Generally the humidity loving Cameroon species such as four-horned and montane chameleons do well in glass sided screen top enclosures. Carpet chameleons will do well long term and have been bred and raised in glass sided enclosures. Jackson's, veiled, and panther chameleons have been successfully raised and kept long-term in larger glass sided enclosures with screen tops. As could be expected the small leaf litter chameleons of the genera Brooksia and Rampholeon generally do well in glass sided enclosures with screen tops. The often mentioned stress of chameleons seeing their reflection in the glass, I believe, is greatly exaggerated. This being said the best enclosures for large chameleons species are large enclosures no matter what they are made of. Keeping larger species loose on indoor trees is even better.
Now, you can argue with this or not but I thought it was interesting.

