Hi and welcome!

Understanding UVB is the hard part. Let’s back up a little bit first. I’m going to apologize in advance if in any way, shape or form I sound not nice.
I do love that you’ve got all live plants. However, I can’t recognize what they are so am wondering if they are safe for a chameleon. If you are getting a veiled, you especially need to be careful since they like to nibble their plants. You don’t say if you’ll be getting a baby and upgrading the enclosure later or not, so I need to let you know that the standard minimum size for adult panther, veiled and Jackson’s chameleons is a 2x2x4’ or equivalent size. It’s a huge size difference as you can see from the pic below. *pardon the fake plants - I was new & learning then. So, with the larger enclosure you’ll be needing a longer UVB fixture of 24” long. The T5 is correct and then you want to use either a 5.0 or 6% strength bulb. This is the standard and it provides the ideal uv index of 3.0 at a distance of about 8-9” below. If using a 10.0 or 12% uvb bulb, the distance needs to be farther to around 10-11” between light and basking branch. To ensure that your chameleon is getting access to the uvb, you want to make sure to keep the area free of plants. You do want to provide some nice shaded areas for your chameleon to cool down and escape the uvb and heat if it wants. I’m adding a pic of an enclosure I set up for a panther a while back to demonstrate. The highest branch is the basking area. I raised plants up on top of empty plant pots turned upside down (making sure all was stable) and later I did add many more branches. You can see how I have my lights on top - 1 is a plant grow light and my basking light was the only bulb in the dual dome.
Give me a little bit to find some good info explaining uvb.
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