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Anne Marie Helmenstine, Ph.D.

Black Lights and Pet Stains

By October 12, 2007

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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) Add to Technorati Favorites

Comments

February 6, 2008 at 6:50 pm
(1) Christopher says:

I actually found that it can depend on what type black light you use. When I use a black light bulb (the one that looks like your ordinary light bulb) I can find no spots from my dog or cat. However if I use one of the smaller handheld black light that have the long slim bulbs (the long bulbs fluorescent bulbs) that every area one of the pets have had an accident shows up. Not sure why there is a difference but there was for me.

April 3, 2009 at 1:48 pm
(2) BRANDI says:

IT DEPENDS ON THE WAVELENGTH RANGE OF THE BLACK LIGHT YOU GET. THE CALL IT NANOMETERS. I HAVE BEEN ALL MORNING RESEARCHING THIS BECASUE OF OUR PETS ACCIDENTS. WE JUST WENT TO LOWES AND GOT A UV BLACK LIGHT. IT WORKED. IT WAS REALLY BRIGHT YELLOW ON THE SPOTS THAT I DID NOT KNOW ABOUT. THE SPOTS THAT I HAD ALREADY CLEANED WERE LIGHTER. SO I THIK IT JUST DEPENDS ON WHAT YOU BUY.

August 14, 2010 at 9:34 am
(3) Meandmythreecats says:

Pet stains are better detected by light of lower wavelengths.
The reason:
Most blacklights on the market are near the 395-400 nM (nanometer) range… which is very close to the visible range (for humans). I.e. no difference in the carpet.

If you buy a blacklight that emits near 375-385, you will be able to detect pet stains MUCH more easily.

November 9, 2010 at 12:11 am
(4) Tammy says:

I agree with the comments… It depends on the bulb. We just bought a new (for us) home (2005). Using the handheld slim flashlight (black light) we have found that there are nasty stains everywhere. Couldn’t figure out why my dog was “marking” in the hall, but based on the stains I found I know now. Was ready to kill my dogs but then I looked in the spare room and master closet. These rooms have been off limits to the dogs since day one. Sure enough, stains everywhere. So, I now search for a product to remove these stains and odors or replace the carpet.

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