So give this a listen.
https://www.chameleonbreeder.com/podcast/ep-91-veiled-chameleon-lighting/ this is based on providing a level between 3-6 for veiled chams. Looking at that chart your gonna be hitting about a 2.6-3.7 ish at 7 inches. The problem is that you lose about 30% through the screen. What I don't like about that chart is that they do not specify if these are the levels with the screen or without screen blocking the light.
I do have a solarmeter. I am running a 12% Arcadia bulb in a quad fixture and am at about a 3.5 at basking level with a rise to about 4.3 at the top of his back. That is using the solarmeter. The hard thing is unless you have a solarmeter you will not know what your levels are exactly. I highly recommend them but they are pricey. What I have seen with doing a lower strength bulb is that so much gets lost with the screen that you literally have to have your basking right below the screen which is dangerous. But this is why it is important to have live plants that they can retreat into when they feel the need.
There are many other great podcasts there you may find really interesting.