Black Lights and Pet Stains

I got an e-mail recently from someone asking about a black light on a carpet cleaner, that could be used to detect unseen pet stains and odors in your carpet. Many body fluids will fluoresce under an ultraviolet lamp aka 'black light'. However, I found it unlikely a black light would be able to show you where you needed to clean your carpet. I sent Ryan, my 11-year-old, on a mission of experimentation. He has a black light, which he uses to display his Lego™ collection. Legos glow spectacularly under ultraviolet light! With pets and kids in the house, it wasn't exactly a challenge to find areas of the carpet that should light up.

What do you think Ryan found? He discovered our carpet is not fluorescent. None of the areas in the carpet known to have been involved in pet accidents glowed. That could just be a testimony to my cleaning abilities. He took the black light to the cat's litter box... no glow in the 'clumped' urine areas, though there were bright dots here and there in the box. The bathroom was interesting. Toothpaste glows brilliantly. So does urine, so any non-clean areas by the toilet were easy to spot.

Based on this informal research, I would guess a black light could be used to detect fresh 'accidents' on a carpet. I would not expect it to detect older areas, unless no attempt had been made at cleaning them. I don't think odors would be caused by a sufficient number of molecules to visibly fluoresce, plus I think some of the problem might be deeper in the carpet, where the light would not penetrate.

Things that Glow under Black Light | Candy Triboluminescence
Photo: Typical black light or UV lamp. (Kallemax, wikipedia.org)