You may have seen the UV flashlights that help spot pet urine. The wavelength of the light emitted is the critical aspect which causes the pet urine to fluoresce. My neighbor runs an AV business and happens to have a theatrical light with a bulb of the same wavelength that he uses for events - the difference being this monster weighs 75 lbs. and throws 600 watts of light. A wee bit more powerful than the typical flashlights.
So I had a friend who suspected that his tenants had allowed their dog to pee in his rental home. They moved out, and we moved in with our light to gets some incriminating shots.
See spots “spots”, with and without the black light.