Photographic plates may be used, although most are too fast and not UV specific enough for your purposes. Also, if your city is quite polluted, they are sensitive to many chemicals in the air, especially sulfur compounds. One approach to extending the UV range of these papers is to add a UV fluorescent chemical such as dihydrocollidine ethyl carboxylate. Another test paper used was made from purified sulfite pulp and dyed with Benzoazurine G. Many of the other chemical detectors require an analytical lab to quantify. In the latter case, a lab is required to quantify the remaining oxalic acid.
Most museums use two devices.
The first is a lux meter for measuring illuminance. Sources with a UV content of 75 microwatts per lumen or more should be filtered. The radiometric devices have no long wave cut-off limit and read right into the IR end. They are also non-spectral sensitive. Photoelectric devices also vary in response depending on wavelength.