When I first was talking to people who (supposedly) knew what they were talking about, many years ago, I was grrssly misinformed. A very prominent chameleon person, and author of a very well-respected book, actually told me that my veiled was sure to die if not exposed to UVB light on a regular basis - several times a week. this person told me to take him outside for 15 minutes a day, 2-3 times a week, as long as it was above 32 degrees - else he would surely die. Freaked me out.
To sum up what I've been saying: Just because a veiled chameleon can tolerate temperature drops near freezing doesnt' mean it's good for them to tolerate temperature drops near freezing on regular basis.
This is NOT to be confused with temperature drops in general, or even seasonal changes. I fully believe the fact that my aniamals get exposed to low temps at night during the year is very benificial - for the deremensis it's crucial. For the calyptratus, it's certainly not harmful.
That said, when my calyptratus were exposed to ~40 degrees nights for a couple weeks, it didn't seem to be good. The adults lost weight, and were stressed for a while.
For all I know, this may be perfectly normal in the wild. If MAY prolong their life and increase reproductive success. It may weaken them and make them live shorter lives. Dont' know.
It's difficult to tell with these animals where the boundry between necessary/benificial and potentially harmful lies.
With my deremensis, I've found that cold-as-heck nights seem to be tolerated very well, as long as the day is warm. My melleri seem to be the same, though they like their days a bit warmer and sunnier (my deremensis only bask int he AM), my melleri are busy all the time.
My calyptratus just seem to endure the cool nights and days until they're over. when they have a cold night, they basked, but they didnt' do much else. They seem to tolerate it, whereas the others were much more "normal" with cold nights.
In the past years, I lot MANY deremensis. All of them were healthy, relativly stress-free, and well taken care of. They all lived well for a year or so, and then just stopped eating. They never got skiny, they just died. They died with a grossly fat liver, massive fat-pads and huge stores of not-yet-ready eggs.
The crazy thing was I was careful not to overfeed them. One cricket a day, lots of mealworm beetles, flies, etc. Low-calorie insects, not much fat. they were not consistently fat - only shortly before death did they plump up.
Problem was, I lived near Raleigh. Kinda hard to get the temps down at night. Especially in summer.
Now, I've been living in the mountains near Asheville. My deremensis get their cool downs, they go through their brumination. They do not eat for days at a time. And most importantly of all - THEY LOSE WEIGHT! all my deremensis got skinny (relativly speaking) this Fall. Late Fall, early Winter, they started to get active again (I warm them up for the breeding season). Now, they're pigging out, and are back to their normal weight.
For deremensis, the cold temps, and the lack of "normal" activity is key. While it's not a great analogy, it's kinda like a bear going into hibernation - putting on tons of fat and all - but not going into hibernation. I think the deremensis do something similar, but they just do very poorly with fatty livers.
Also, I spoke to Josh Ease a year or so ago about this. He remarked that after the winter, most of the deremensis were emaciated. While we don't have to make things so extreme in captivity, we do need to replicate some of these stresses if the animals need it.
It's my experience that veileds do best with drops in the 60's or 70's at night. Don't know if colder temps or long cooldown periods have a positive or negative effect on individuals. Thoguh I can attest to the fact that days after a cooldown period (that lasts a couple weeks) females become receptive and males become energetic in their courtship displays.
I'd suspect that many veileds that are not good breeders could benifit from a seasonal change or two.
Go here and click on Sana'a and Ta'izz. 
I'd be interested to hear if others have found similar results in necropsied calyptratus, especially the condition of the liver. 
