So, a great site for uvb information for equatorial species is
https://www.madcham.de/en/.
The site is dedicated to Malagasy species, but there’s some pretty good uvb data there. Because light decreases with the square of the distance, higher altitudes will always see higher uvb levels. There are several European keepers, eg Mario Jungmann, who use higher uvb levels for their montane species. Check out the chameleon breeder podcast episode 127.
I haven’t done the kind of uvb research that I dedicated to my blogs about vitamin A and gutloading—mostly because much of the info is accessible, and better understood.
All that being said, I think some critical reflection can yield dividends here: chams move throughout their biotopes; the wind moves foliage on a random basis, and prey items appear in such a way as to necessitate sun exposure/shade. All this happens while the noon equatorial sun is putting out uvi’s of 12-13. This suggests that as a shading leaf moves in the wind, and as chameleons move throughout their environments in search of prey, they get struck with full sun to full shade. Anyone who goes for a walk in the park can attest to the fact that every movement they make exposes or shades them from the sun. Given this, I find it highly intuitive to provide dappled partial shade with high uvb levels in my enclosures.
I should add, though, that I don’t use any d3 in my supplement regime.