Where is my pet's hidden stain?

Why Does My UV Light Not Make Urine Glow?

Occasionally customers have issues locating pet urine with their PeeDar or other blacklights. Here we’ll detail how to quickly check your light works, then we’ll provide a more in-depth look at all the major causes of reduced fluorescence, and finish with some key methods of identifying the source of a glow.

Before you go any further, first ensure your PeeDar’s light is a constant, strong light blue colour on standard white printer/writing paper.

Is Your UV Light Fully Functional?

All LEDs should be producing light of roughly the same intensity. If not, or you believe your unit is faulty in some other way, contact us and we can discuss issuing a free replacement!

Reduced/non-existent fluorescence is most likely to have come from some or all of the following:

  • Insufficiently dried urine (the usual culprit!) – as it dries urine starts to increasingly, constantly, wick water moisture from its surroundings, whether it’s in a liquid form or moisture in the air. Humid air (e.g. from bathrooms, kitchens), wet absorbent materials, and regular pet urination (esp. larger animals) in/near the last urine patch can significantly reduce glows, in some cases to zero.

To see glows, secure the suspect area from animals/people/moisture-producing things so it has time to dry. In cases of potentially large amounts of urine, such as when it has seeped through many layers of carpet or deep into furniture you may literally need to dry the area for a few days, or up to a week at normal room temperature. Dry urine has a much more crystalline structure which is able to provide the greatest glows possible. If you can stomach the smell, faster drying may be achieved by novel methods of removing moisture, e.g. hair-drying or using a portable filament heater safely and carefully aimed at the edge of a wet stain.

Moisture meters are a good extra tool for locating wet (or dried – due to its wicking nature it is always at least a tiny bit wet!) urine. You can also ask your vet about “fluorescein”, it’s ingested by your pet, and peed out over a few days, fluoresces very brightly in wet or dry urine, and has the added advantage of being able to reveal individual problem pets and where they go. Remember too that neighbour’s pets can sometimes be the source of your urine woes. Cats have been known to visit other people’s homes to eat their pet cat’s food, amongst other possible antics. Dogs sometimes urinate in other people’s homes, such as when a dog owner invites a friend’s nervous/territorial/poorly trained dog round to play with their own dog.

  • Low surface areas of dried urine – carpets have much larger surface areas for urine to dry on and then react with UV. Tiles, on the other hand, often emit less glows due to thinner layers of urine, and the ease with which urine can be cleaned/worn away.

Dried Urine On White Bathroom Tiles Under PeeDar 2.0's 380-385nm

  • Majority of urine absorbed below the surface – common on furniture as well as other highly absorptive objects, urine can be absorbed deep below the surface with very little if any detected at the surface.
  • Used/low power batteries – PeeDar LEDs use a lot of battery power. Used batteries can deliver markedly lower UV light output and therefore the resultant weaker glows can make finding urine stains difficult.
  • Urine that naturally fluoresces very little – some pets are reported to have urine that naturally doesn’t fluoresce much if at all under UV, and usually not much can be done about this. Ingestion of large quantities of water is known to cause pets to pee out the chemicals in urine that create the yellow colour that seems to be responsible for fluorescence under UV.

One way to assess glow strength is by absorbing wet urine onto dry white tissue, shining your PeeDar on it once dry. Weaker glows will let you know searches should be slower and more methodical.

  • Dark or patterned surfaces – darker colours absorb more light, reducing glows. During tests we’ve performed dark carpet colours such as deep blue and rich red did prove problematic, some glows were not detectable! Patterns make seeing edges of glows more difficult. Other types of glowing stains that cover suspect areas, such as those from cleaning fluids or some types of food, can also add to the confusion.
  • Similarly glowing surfaces – although we’ve yet to see this, the sheer range of carpets on sale inevitably mean that some may glow with near enough the same intensity as your pet’s urine, this could make detecting contrasts, especially with weak glowing urine, quite difficult. Lighter coloured carpets, often of the same colour as dried urine, could create glows under UV.

Interestingly, at least from our experience, whitish coloured carpets (see our product’s before and after photos) are great for detecting dried urine. Lighter flooring colours naturally reflect more light away through the dried urine, this filters much of the visible light into the glow colours of the urine. Outlines are also more visible since the glowing surrounds are strongly a different glow colour to the urine. Such lighter carpets also have the added bonus of actually showing up some stains in normal daylight.

  • Incorrectly tinted glasses – from tests we’ve performed, under 385nm any tint colours/shades in glasses, UV-protective or not, reduce the contrast of stains against their backgrounds, making stains harder to spot. We recommend using zero tinted 99% UV protective safety glasses when hunting for invisible urine stains with your PeeDar flashlights. If you’ve got a cheaper 390nm+ UV flashlight then we’d generally recommend yellow/amber coloured safety glasses, they tend to increase the contrast by cutting out the normally overpowering obscuring strong purple visible light.

Clear Tinted UV Safety Glasses

  • Not searching in complete darkness – although obvious, only by searching in pitch black conditions will be give yourself the chance of seeing the full spectrum of glows, from bright and intense colours to the very faintest glowing older stains.
  • Not searching in the right areas – sometimes you’ll smell the stains yet see nothing. This could well be because you simply have not looked around hard enough! Pets can appear to be very creative with where they urinate. Cats in particular can sometimes pee in the most seemingly unlikely places, such as on book shelves, behind doors and under tables or settees.

Lastly, finding the source of the glowing material can be difficult, UV lights simply highlight all fluoresce-able substances. We know that urine in general has a mid-to-low intensity glow compared with other fluorescing things, and is a light yellowy-white/straw colour. Cat urine can often have a faint light green tinge. Cat urine glows usually have spray or pool-shaped outlines, sprays are usually on more vertical surfaces, regular urination is typically on horizontal surfaces. Cat urine often has a very pungent ammonia smell too. Dog urine reportedly usually has less of an ammonia stench, older stains can sometimes not give off much smell, but generally all urine is usually unmistakable when sniffed close enough. Dog puke can appear as a dull/faint yellow/mustard colour. Cleaning fluids have among the strongest glows possible, often from their bleach component, and are usually a brilliant white or whitish purple/blue. Food glows are highly variable, from nothing to extremely vivid (e.g. Thai green curry glows a very strong straw/light greenish colour). Some juices such as orange juice show up as a deep red. This is a complex area as you are probably beginning to see.

Thai Green Curry Under PeeDar 2.0's 380-385nmOrange Juice Fuorescence Under PeeDar 2.0's 380-385nmDog (Young Male Cavapoo) Stain Under PeeDar 2.0's 380-385nm

When using your PeeDar with our advice and your natural senses, we’re sure you’ll be able to locate and eradicate all your pet’s mistakes with relative ease. Please do tell us how you get on!

11 replies
  1. Melissa Sams
    Melissa Sams says:

    I purchased the PeeDar 365-370 LED flashlight and put it away,last year, and then found my toy poodle had soiled my rug as not only could I smell it, when I pulled the rug back (it is an area rug), I found lots of staining on the pad. I had the rug professionally cleaned, but I found some new spots on the pad recently as again smelled an odor. I recalled getting the PeeDar, put it new batteries, tested it on white paper for the blue glow, but despite using it the dark with curtains closed, cannot find the stains on the rug. It is patterned rug with a white backround. I have even tried using my prescriptions sunglasses with no differnce.Any suggestions as I know the urine is there?

    • admin
      admin says:

      Hi Melissa,

      Many thanks for your message there, it does sound like you have a few obvious and smelly patches that should be lighting up nicely, let’s see if we can help you here! As a matter of thoroughness could you let me know if you’ve read all of the article you placed your comment on, and firstly, ensured that the urine was dried? Unfortunately the best way to do this is by getting a dry white piece of tissue paper and dabbing it a few times, in a very slow and deliberate manner, with some downward force, on the various perceived soiled areas, especially what you regard as the centre of the urine spot. If moist urine is present is should stick to the dry tissue, even the presence of very small visible droplets of moisture are a sign that more drying could be a good idea. Sometimes it may take a few days to dry the urine patches off (without your pet topping them up a few times each day) by closing off the area to all animals and any cleaning/moisture-introducing attempts.

      Your dog’s faeces won’t glow, and may cover some of the glows, in addition the patterns on your carpet may break up the contrasting edges of any glows. The white background of the carpet should glow very strongly generally, this usually means stains on it will be much stronger too, although there can be the rare case of a more unusual material simply not glowing much.

      Prescription sunglasses won’t help regards finding stains at all unfortunately, they will only act to make spotting anything more difficult. The PeeDar’s super low UV range doesn’t require any visual aids, such as amber coloured UV safety spectacles, to improve spotting stains, glows are more varied in colour and stronger without.

      I’m pretty sure you’ll want to get rid of the stains quickly, when you’re having trouble seeing glows under UV moisture meters (these detect both dried and wet urine) along with your natural senses are best for locating stains to cleaned with the appropriate quality enzymatic pet mess cleaning solution. Fluorescein, a harmless dye swallowed by your pet and peed out over a few days, glows extremely strong under UV even when wet, ideal for when moisture may be affecting fluorescence, or pet urine is simply not that glowable. Ask your vet about this dye, he may be able to provide it.

      Please let us know if you’ve tried the above advice, we can then move to the next stage if required.

      Best regards

      Steve Grzywacz
      [Co-Founder – Urine Eradication Systems]

  2. AJ
    AJ says:

    This was the most informative … um, tinkle teaching site I’ve seen yet. I’ve spent hours. Also, kudos on being so wonderfully explanatory as well as informative! This is Uber confusing to me and I had a science degree. However I couldn’t defend an argument tonight that my parents were incorrect in their belief that a fluorescent light and a black light were the same thing, not to mention all the differences in how stains will show up. I learned so much, and feel a little more steeled in the next argument I’m sure to have with them regarding this! I’m joking (somewhat) – a dubious reason for learning such valuable information, but I truly will retain this for myself as well, since I see myself always having kitties (though, I hopefully won’t need to necessarily employ said knowledge). Either way, wonderfully written article for such a complex subject, and fantastic tips to boot. Well done! My grateful thanks.

  3. Katelyn
    Katelyn says:

    Are there specific UV lights that detect pet fluids such as their urine or is it all UV lights that show bodily fluid? Also even after a carpet had been cleaned several time with a carpet cleaner could spots still appear under the UV lights?

    • admin
      admin says:

      Hi Katelyn,

      Many thanks for your message. As far as we what we’ve seen, regards urine specifically, 380-385nm appears best for highlighting dried cat and dog urine. This seems largely due to certain chemicals in urine reacting with the UV to give the greatest quantity of visible light, the sheer quantity of UV, and very low amount of visible light, produced by the LEDs. We haven’t tested UVB lights, but we’re pretty sure all standard UVA (315-400nm) lights should create useful glows on the majority of pet urine.

      We can’t with as much certainty say how effective UV is on other types of pet fluids. Judging from how some deep red food fluids have appeared in the past, e.g. red wine, if on a lighter coloured background blood may appear as dark/black patches. Our customers say semen is highlighted, I’ve seen dog puke be a very faint light green/yellow, faeces doesn’t seem to glow at all.

      We were going to release a powerful enzymatic cleaner of our own, but during testing of some brands they didn’t always remove glows from urine stains. I’ve heard that some enzymatic cleaners do completely remove all traces of pet urine, including the glows, this may be true, but we haven’t experienced that ourselves yet.

      I hope this has been helpful, and if you have any other questions just fire away! Good luck with your stain hunting and removal.

      Best regards

      Steve Grzywacz
      [Co-Founder – Urine Eradication Systems]

  4. Lucy Tran
    Lucy Tran says:

    What do you suggest to do with dark carpet?? I have a UV light, but it’s not picking up the urine stains. Is there glasses or some kind of spray that will make it show better? Ive blacked out the room and it still doesn’t help. I currently do not have any kind of goggles/glasses

  5. Robin
    Robin says:

    My daughter just recently had her carpets checked for cat soiling….. when the man scanned the carpet he found 5-6 areas that glowed (I could barely see them) they were very small areas. I have never known her two cats to ever mark or have an accident. However, my daughter was on TPN at home for 4 months. Could drips or small spills caused the markings? Every bag did contain sodium phosphate and we remember making the comment that the TPN smelled like cat urine. Don’t want kitties blamed when it was not them.

    • admin
      admin says:

      Hi Robin,

      Many thanks for your good question. We’ve never tested TPN bags to see if, and how much, they glow under UV, but there is a chance their contents could glow. Many different types of food and drink glow under UV. The fact that you’ve never noticed your cats having urinated inappropriately before, combined with the very weak and small sized glows of the suspect areas under UV makes me think the fluid from the TPN bags could’ve been the source. Cats that urinate inappropriately do so in a particular way (e.g. a spray on more vertical surfaces at cat height, or pool or slight tear shape on the ground), and usually in the same places (therefore the patches would typically be of a noticeable size/smell). Providing the glows you found were in areas that the TPN bags could’ve been used, TPN fluids could well have been the source. Scanning your whole home, not just the carpets, for stains would help you gain a better idea of where they came from. If similar stains, for example, were in hard to reach areas that only cats would potentially go to, you may have the answer you were looking for. Also, if the glows are not white, straw or whitish-light-green in colour, but instead a strong blue, for example, they are likely to be from a different source, in this case bleach from cleaning fluids. Becoming a bit of a detective is a necessity when determining the source of glows under UV, UV simply locates stains!

      I hope we’ve helped you here, do let us know how you got on, and feel free to ask us more questions if you have them.

      Best regards

      PandoraStocks LTD Customer Support

  6. Stephanie
    Stephanie says:

    Once you treat the urine stain adequately, will it cease to glow? I have no sense of smell to tell if an odor remains.

    • admin
      admin says:

      Hi Stephanie,

      Many thanks for your question. Although stain detection is our business, we have learnt quite a bit about the even more complex area of cleaning up afterwards. If you’ve used a good quality enzymatic pet urine cleaning solution, such as Urine Off, Nok Out or Anti-Icky Poo, applying the solution as instructed and repeating, if necessary on stubborn/older stains, up to 3 or 4 times, all of the urine stain’s ingredients should be completely eliminated.

      When applying enzymatic cleaner, make sure to drench the area affected. Also, it is always a good idea to mop up as much liquid urine before any cleaning, and as much of the cleaning fluid as possible after the required amount of time for the cleaner to do its job has elapsed.

      Non-enzymatic cleaners/cleaning methods don’t adequately remove urine stains, typically at the very least the non-water soluble uric acid and salts will remain. When these components come into contact with moisture they form uric acid crystals, this process releases odours which, although sometimes too faint for owners to smell, will often be detectable by your pet, and so promote re-offending in the same area. Uric acid is said by some sources to have a half life (time it takes to reduce in quantity by one half) of 6 years if left alone, so it is very important to completely remove this particularly stubborn part of urine.

      After adequate enzymatic cleaning there should be no glows present from the stain at all. To maximise glows after cleaning, make sure you’ve given the cleaned area plenty of time to fully dry before using your PeeDar in the dark! Since you can’t smell things that well try and get a friend or partner to see if there are any smells remaining, or recurring after a week or two. You can also see if your pet detects the area, they typically hang about and sniff the area a fair amount if there’s something interesting (it could just be that new, interesting smells are now there though!). This is slightly off-topic, but the use of ‘fluorescein’ can help if your cat is re-offending, this is a harmless chemical dye that is placed on pet food and ingested, peed out over a few days. This dye glows a brilliant brighter urine colour even when wet, and can show where your pet has been urinating. Lastly, the use of a moisture meter can help detect suspect wet patches on or near cleaned areas.

      I hope you’ve found this advice helpful, and we wish you the best of luck with finding and eradicating all your hidden stains. As always, we’re on hand to try and help, so do let us know if you have more questions.

      Best regards

      Steve Grzywacz
      Co-Founder – Urine Eradication Systems


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