UVI 3 is the one UVI level that has been tested within the community to provide enough vitamin D synthesis for a female Veiled or Panther chameleon to produce a fully calcified clutch of eggs with no dietary vitamin D3.
There has been no observed benefit shown at UVI 6.
UVI 3 has also been shown to be a good level for baby carpet chameleons.
The only thing magic about UVI 3 is that it has been tested on chameleons repeatedly by multiple people. Ferguson zones are a collection of extrapolations, data, and logical estimates. But the work done within the community is actual UVB on actual chameleons in captive situations.
UVI 3 is not the end of the story. It is only how far we have come at this point. Every couple of years someone else adds more to the story and we get a better picture. So far UVI 3 is holding as a functional target for the basking branch. Since tests have been done to show no additional benefit at UVI 6, but no detriment, that is a good enough selection for the upper limit. There is nothing sacred about UVI 3. It is used as a baseline because that is the most tested data point we have. Something has to go on the care guides. It makes sense to use a value we know works until we know something better.
There are no "leaders" and "followers" here. Just explorers and people trying to figure things out. If anyone wants to add more to the story the only thing in your way is a whole lot of tedious and meticulous work. We do not know what the lower effective level is. And there is much work that can be done with dose (intensity x time). UVI 3 at 12 hours a day works. Will UVI 3 at 1 hour a day work as well? Chameleons can detect UVB and have been known to UVB bask. Can a female lay a fully calcified clutch of eggs with UVI 3 only one hour in the morning and no dietary D3? And some people wonder if UVI 6 at 30 minutes is the same as UVI 3 at one hour. That particular test is not of interest to me, but it would answer an interesting question. The only requirement in all of this is that your test have an objective way to measure results and be able to be repeated by anyone to get the same results.
If you would like to repeat the test yourself, get yourself a gravid panther or veiled female, measure UVI 3 a couple inches above the basking branch (back height) and offer UVI 3 for 12 hours a day along with the rest of the normal husbandry and nutrition. Then see if the eggs, when laid, are fully calcified. If this is not a good enough way to test the results then do blood tests or whatever else satisfies your curiosity. The calcification of eggs was picked because that was a practical result we care about and we know if the female does not get enough calcium that the eggs will not be fully calcified. Someone will argue that we don't know how much calcium was taken from her bones and I will say that I would be excited to see the next experiment that uses blood tests or whatever else is a better measuring stick. Please poke as many holes as you want in the test or the conclusion, but also use all that energy to put together a better test and perform it yourself so we can all benefit from the results. Building on what was done before and making it better is not an insult to what was done before. It is the nature of science to build on past results with better and better tests. So, please, challenge UVI 3 and whether you confirm the results or provide more insight into practical application of UVI in the captive environment, the community will benefit.
