[header] How to find cat urine with a uv light [title] Buy a decent-sized uv or " fluorescent black " light. [step] Look for a long bulb (preferably longer than 12 inches) so you can cover more ground at once. Cheap bulbs with the housing included can be found at most hardware stores. 
Although pet stores sell the lights as well, they're usually smaller and more expensive. They can also be purchased at a reasonable cost online, depending on how much time you have to wait around living with the odor.