I'm not aware of any uvb strip lights that work on a dimmer stat, especially not a uvi dimmer stat?? I don't think that going from 1 light to 2 lights to 3 lights and back down to 1 over the course of 13 hours is a completely unnatural flipping of lights on and off that is going to unduly stress my cham out?
The enclosure is in an outbuilding so I'm not unduly concerned about damp.
Monthly rainfall is between 80mm and 250mm which is 3mm to 10mm per day. From observations I have found so far, panthers tend to hide away from the rain so there is likely little benefit from fully recreating monsoons.
I currently have 4 Internet connected sockets and a controlling hub for £50.
So a few things with this. So lets break it up

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"I'm not aware of any uvb strip lights that work on a dimmer stat, especially not a uvi dimmer stat??"
By UVB Strip Lights, you mean Flos correct? If so, all of them would work with a Dimmer Controller, the issue is not with the light, its the ballast. There is Fluorescent Dimmable Ballasts available, they are not cheap and they do not work with a Dimming outlet, as I think you mean. They use 0-10v dimming system, their is lots of options for that on the Market, alot of which will also work for LED systems. The Apex I had mentioned, was one such device.
Now I would not, partake in doing such a feat without a UVI meter at the least, and really you would have to. You would need to be able to know how much UVI your lights pump out at what percentages to be able to match that to the UVI data. This would allow you to sculpt a recreation of the daily UVI, however not on point on day, but we will come back to that.
"I don't think that going from 1 light to 2 lights to 3 lights and back down to 1 over the course of 13 hours is a completely unnatural flipping of lights on and off that is going to unduly stress my cham out?"
Although I am in the minority, I would say it fully will. We dont have enough people attempting to recreate natural light to really know for certain. We do know that Chameleons and all reptiles, get most of their Qs from the Sun, they are more perceptive of changes of color, placement, brightness, ect then we are.
I have a post about this I have been meaning to write up. However the jist is pretty much that. An article that shines this theory can be found here (I been linking this alot as of late lol)
http://www.reptilesmagazine.com/Reptile-Health/Habitats-Care/Reptile-Lighting-Information/
An Excerpt if I may.
"Sunlight also has effects unrelated to conscious vision. A reptile’s eyes, and the parietal eye (third eye) in those species that have one, transmit information to other parts of its brain responsible for setting circadian (daily) and circannual (yearly) rhythms. There are even light-sensitive areas of the reptilian brain that respond directly to sunlight’s glow through the skull. The length of day and night, the sun’s position in the sky, and the intensity and amount of blue in sunlight all give precise information about the time of day and season of the year. In response, a reptile adjusts its activity levels, and daily and seasonal behaviors, such as its reproductive cycle and thermoregulation needs. Even nocturnal species govern their behavior by monitoring day and night from their daytime hiding places.
No artificial lighting system in the world can provide the full spectrum and intensity of natural sunlight, its subtle changes in color as a day progresses, or the sun’s movement across the sky. For these reasons alone, the more natural daylight a reptile experiences, the better."
I want to be careful talking about this, until my post is finalized. As I was accused of anthropomorphizing speaking about it the other day. However, I will still apply that same excerpt.
How do you feel when you are asleep and someone flips a super bright light in your face? Now this is where I was anthropomorphizing, however its not anthropomorphizing at all. That is an instinctual reaction to flip up in a state of panic and stress from such an event. It is not something humans alone solely posses. Reptiles, especially chameleons hide stress very well, until it is immense. However the fish guys, have begun to move away from flipping lights on, as they are clearly stressed by the endeavor. Want a easy test? Got a dog? Go shine a bright light in their face while they are asleep and watch how fast they hop up in a panic.
Now the excerpt had an aspect of importance due to its old age.
"No artificial lighting system in the world can provide the full spectrum and intensity of natural sunlight, its subtle changes in color as a day progresses, or the sun’s movement across the sky."
The article is old, we can 100% do this today, and you with your shaped corners can even move the sun throughout the day, something most of us do not have the luxury for, if you were so inclined.
"For these reasons alone, the more natural daylight a reptile experiences, the better."
Right, so why are we still flipping lights on full blast first thing in the morning like its 2008

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Sorry for the rant, I need to finish my post, which might have to be a Blog due to the (I feel new?) 1000 char limit lol.
"Monthly rainfall is between 80mm and 250mm which is 3mm to 10mm per day. From observations I have found so far, panthers tend to hide away from the rain so there is likely little benefit from fully recreating monsoons."
I am slightly in agree, and slightly not.
I do agree that for the most part, most of the time, they do not like the Mist. However, I have been melding the lighting ideas with that of the mister and found something of interest. I dim my lights before the mist, to simulate the cloud before the rain, and will be adding more to that simulation soon. When this happens, my Panther does seek a leaf, or shelter from the mist at times, its been slow but he is seemingly learning what that means. Sometimes however, I have a few times witnessed an opposite behavior, he seems to move towards the misters, and plant him self firmly in where he knows it to spray. Usually when doing this, he will hide his head, and sit there until the mister has started and ran its course. I see this behavior alot before a shed, sometimes he will too back his head in and seemingly wash his eyes.
I know that others have experienced this as well, on these very forums. Chameleons do not always seemingly to run from misters, they in my experience always do, at first, without the lighting changes, however they ease back into the mist after the stress seems to have subsided of being blasted with cold water out of nowhere, I know I anthropomorphizing again, Animals dont realize when they are blasted with Cold water

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That all said, I dont see a reason to recreate hour long monsoons either lol. I think, though I dont know as I have not studied the weather in Sambava much, that is quite like the upper and eastern forests anyway, more short bursts of rain throughout the day, then it is pure hardcore downfalls you would likely no more about that though.
Anyway, so then I feel I am not truly understanding the idea at hand? Was it to created a schedule based on days, but a schedule none the less? Or a system that uses the current location based weather data and recreate it live? As their is systems that can do the later, but then if it rains for 4 hours and rain sets off the misters, then it will run the misters for 4 hours. That was what I took from your post, as was your intention. That was why we are back to the UVI, I had thought you meant the same as with the misters. So whatever the UVI is at that point in the day today, (or yesterday) is what your UVI would be, a controller that could determine and alter that function. That might be fully possible, if you had UVI readings source, and a controller that was coded to do such a feat.