Cat urine glows under UV light, so you can find the exact spot with a UV flashlight shining at a wavelength of 365-385 nm (that's the scientific specification of where on the ultraviolet spectrum the light exactly is).
A lower rating won’t be strong enough to light up the cat urine, and a higher rating is too similar to natural light to have an effect.
- You can find these lights online or at a local home improvement store.
- You can also find UV lights with fluorescent bulbs. As long as it’s rated between 365-385 nm, this will work as well, although the LED lights tend to be stronger.
Wait until it's completely dark outside, then turn off any lights in the room but the UV light. The glow is too weak to be seen when other light sources illuminate the room.
Be aware that there are many other substances that glow under UV light. Urine glows yellow or neon green and you still have to smell the stain to be sure it's urine.
See detailed instructions and more information in this WikiHow article.