First, darken the room as much as possible – the darker the room, the easier it will be to detect the dried urine.
Dried urine has a characteristic dull yellow fluorescence or glow when exposed to LED lighting. This will help you to distinguish it from other compounds that may also glow. For example, some soaps and detergents will leave residue that glows bright white to an almost blueish white, and lint can glow a very bright white.
One way to learn the characteristic color of dried urine is to take your Urine Finder into the bathroom and illuminate the toilet and surrounding area. Even in the cleanest bathroom, you should be able to see the dried urine crystals that conventional cleaners cannot remove.
Another way to distinguish dried urine from other compounds is by the shape and location of the stain. Urine stains are generally found in predictable locations, like corners and at the base of furniture, and will have a shape that resembles a puddle or a stream. If cats are involved, be sure to check the baseboards and walls for traces of spraying.
Keep in mind that if the urine was already blotted up or has seeped down into the carpet and most of it has been cleaned off the top layer of the carpet (in the fibers), then it will be harder to locate with the Urine Finder. In such cases, it may be wise to pull back the carpet in the areas you suspect so you can be sure you’re not missing any smelly spots.