Hi. There has been quite a lot of discussion over the the years about the value of UV testing. Some people believe it can help with ID, others think it is so unreliable it is a waste of time. What you do is shine UV light (of whatever wavelength the light you buy emits, and this can vary) onto the glass. This can excite fluorescence in the glass, depending upon what metallic elements it contains, and how these are bound within the glass structure. Users then look at it and make a purely subjective assessment of the colour and strength of any fluorescence(with descriptions such as 'pale straw colour' or 'misty blue' etc). So different people (with different eyes) can give very different descriptions, especially if they use different make lights. A detailed scientific study around 50 years ago showed that the UV fluorescence of the same glass can vary, depending on the gases in the glory hole at the time of production. In my view, it may be useful for telling you whether something is lead glass, but that is about it.
alan