If you're using the "Stink Finder" it doesn't put out enough light to see urine spots unless you're withing six inches in a completely dark room. The black light sold by the makers of the "Urine-Off" spray cleaner works MUCH better. It's a pocket-sized black light, too, but the UV put out is a different wavelength or something and it's much easier to see urine spots. I asked them to tell me what the difference is in the flourescent tube so I could buy a large one and make my own light, but they wouldn't tell me. It's proprietary technology, I guess. If you google for it, you should be able to find it sold online.
You can also make your own large black light with an under-cabinet light fixture and a UV tube in a size to fit it. That works better than the Stink Finder but not quite as good as the Urine-Off.
Something else to keep in mind is that lots of things glow under UV light. The key to finding a urine spot is the color (yellowish-green) and the shape (obvious). I was able to find all the places where my cats had vomitted and been "cleaned up." (Not so good, I guess.) And if you really want to gross yourself out, shine your black light in your kitchen or in your bathroom.