UV meters are fickle. The problem is that not all UV is created equal, and the differences are much more pronounced than they are in the visual spectrum. Differences in the spectrum itself if you're talking about sunlight (direct, shade, light clouds), transmission of optical elements (lenses/glass), the sensitivity of the target process (iron salts, silver salts, diazo, dichromate etc.) They all make very huge differences.
Then there's the issue of sensor spectral sensitivity. There's no agreed-upon standard of what the spectral response of a UV meter should be. Every sensor manufacturer just makes their own choices depending on what is technically feasible and what they believe might be useful. Take for instance these plots, that are the 3 sensitivity curves of a single AMS sensor and a low-end ML8511 sensor overlayed on top of each other:
Note how totally different they are, and in particular how the cutoff is at each end.
So you can meter UV, but what does the result tell you? In reality, you can only really say something sensible if you also know spectral distribution, the spectral sensitivity of the sensor, the transmissive qualities of the optical elements used and the spectral sensitivity of the recording medium. And even then you'll be juggling too many parameters to make really good sense of it.
This is not like a regular light meter for visible light photography, where there's an ISO standard and a reasonable expectation of uniformity across different meters. With UV meters, you'll be stumbling in the dark, although you may
feel you know what's going on. In reality, you don't. It's perhaps even trickier than actually not knowing for sure what you're dealing with - at least you'll then be aware of the uncertainties involved!
The only applications where UV meters really make sense is where you can reasonably well control for the parameters I mentioned. In a photographic context, e.g. alt. printmaking in the sun or under different artificial light sources, the usefulness of a UV meter is very, very limited indeed.
There are several/many offered on Amazon, in the $150-250 price range.
I feel that's a lot of money for something that effectively has the dependability of captain Jack Sparrow's compass - but without the entertainment value.
