I would recommend that you buy
a solar meter that measures the UV index.
If you want to save money, then pay attention to the UVB meter at
this link.
I bought this one and have no complaints about its work. It comes with a document on its official verification.
Here, on the forum you can find information on what should be the UVI for the basking zone, as well as the UVB radiation power in uW/cm2, if you decide to purchase a UVB meter
If you are interested in something specific about the UVB meter, then you can ask me about this device, I am always happy to help