Color temperature of lights - demo (C) D FriedmanHow to buy & use a black light, UV light, Woods Lamp for building investigations of animals, odors, urine, blood, other contaminants

  • BLACK LIGHT & UV LIGHT USES - CONTENTS: How to use a black light (ultraviolet lights, bulbs, flashlights) or UV light to track down the location urine and other animal indoor contaminants. Catalog of materials that fluoresce under black light (UV light) & sources of UV lights, supplies. Using a black light to find sources of indoor building smells and odors from dogs, cats, rodents, bats, unusual pets, and even people can be tricky; here are our suggestions.
  • POST a QUESTION or READ FAQs about how to use black light or UV light or a Woods lamp in building investigations

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How to use a black light or UV light:

This article describes uses of UV light in building investigations. We describe the use of a black light, UV light to screen buildings for pet urine or urine from humans or other animals even where no stains are visible in or around buildings.

We also use UV light to screen buildings for other body fluids, including blood. Small black lights are available from pet supply stores, art supply stores, and forensic and police equipment suppliers and are generally inexpensive.

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Guide to Using Ultra Violet Light (UV light or "black light") for Forensic Building Investigations

One of the most effective uses of UV light in building investigations is the tracking down of odors & contaminants such as urine, urine stains, or odors & allergens from pets, rodents, or other animals, even human. But because a large number of materials will fluoresce under a black light, we need to give some thought to how to interpret what our UV light is actually revealing when we shine it on a building material or surface.

Article Contents

Watch out: While in our OPINION the ordinary use of UV flashlights and UV lamps for purposes of building or environmental inspection or security screening constitutes no unusual health risk, excessive or inappropriate exposure to high levels or protracted durations of ultraviolet light may be unsafe and possibly carcinogenic. A much cited study indicated that "The risk was not significantly or consistently raised for exposure to fluorescent lights at home or at work."[12]

Question: using a black light to track down iridescent powder substance in carpet

direct lighting hides problematic light colored mold colony on this wainscot panelingCan you be of help identifying a carpet (?) problem I am having in my apartment?

I discovered this as I was using a black light to look at some iridescent fishing lures the other evening. I noticed several yellowish glowing spots in the bedroom carpeting. This caused me to check the living room and dining area carpeting, where I found the same type yellowish glowing areas.

The areas are ‘dusty’ in appearance and appear in a variety of patterns. I further checked the baseboards, some less trafficked areas behind the bed and other furniture, and the furniture and counter surfaces and found the same yellowish areas.

It quickly returns after cleanup. These areas do not appear in normal daylight, but do appear under a black light. Of course, the iridescence is greater at night when I can darken the apartment, but it can be seen under the black light during the day. It should also be noted that my feet and toe nails show the same yellowish glow. I walk around bare footed in my apartment.

Bathing removes the powdery substance from my feet and my physician says I have no mold or other infection in my feet. It should also be noted that when I purchased my black light over a year ago, for fun I checked out my apartment and carpeting for mold, pet urine, etc. and found none.

I will be checking with a local 'home' inspection type company next week regarding this.

Thanks for you help, - J.N. 07/21/2012

Reply: What materials glow under UV lighting & what is a "black light"?

Black light bulb (C) Daniel FriedmanA competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem concerning building contaminants or conditions. That said, there are a number of materials that will fluoresce under an ultraviolet UV or "black light", even clean white sheets appear to do so.

At above left we illustrate our darkroom test set-up for light source comparisons, in this case with a "blacklight" or UV ultraviolet light bulb (Woods lamp) installed in our test fixture using a 13W bulb produced by Feit Electric (photo at left).[5]

You may have spotted pet urine stains and pet urine-contaminated dust from carpeting, or insect fragments, or possibly some urea-containing materials.

The observation that many materials contain fluorescent molecules means that interpreting light or presumed stain patterns needs to be done with some sense of location, age, material, and context.

Definition of Fluorescence & UV lights or black lights - the Woods Lamp

We should explain the mechanism of fluorescence before listing things that fluoresce under black light or really UV light: According to a nice Q&A by the U. Illinois physics department, although infra-red and ultraviolet spectrums or frequencies are beyond what the human eye can see (some animals can see in these light frequency ranges),

Some materials have the special property that they absorb ultra-violet light and then re-emit the light at lower frequencies that our eyes can see. This is called "fluorescence. [3]

The actual wavelength of black lights or UV bulbs that operates in the UV range is 280-410nm usually narrowed to 368-371 nm wavelength light. Because UV flashlights or bulbs may also emit some energy in the wavelength range that is visible to humans, when you plug in a lamp that contains a "black light" bulb, it won't appear to emit zero "light" (that you can see), but it emits so little light in the range visible to humans that these bulbs are popularly called "black lights".

How to Use UV Lights for Surface Inspection

We have had a number of discussions with forensic investigators and building inspectors, have tested several UV light devices, and have experimented with the forensic use of UV light in our lab and in the field. And of course there are numerous expert sources for this topic.

In general inspectors find that you can use a good quality ultraviolet light source even in daylight (notice the use of small UV flashlights for document checks in airport security screening procedures). But for weak or dilute sources of fluorescent materials, such as very dilute fluorescein septic dye that might appear in a waterway up to a week after a septic loading and dye test, screening the target using ultraviolet lighting under low light or dark conditions is still more effective.

Catalog of Materials & Products that "glow" or fluoresce under Ultra Violet Light - UV light, Black Light

Cat in the house (C) Daniel FriedmanHere is a list of examples of fluorescing materials you might commonly see during an investigation inside or around a building. In parentheses our c=XX note indicates common colors you will see from each material when it is exposed to ultra violet light in a dark area. Use a UV flashlight, a "black light" bulb in a portable light fixture, or similar equipment to screen for these or other fluorescing substances in and around buildings.

  • Animals of various life forms such as some scorpions (emperor), jellyfish (colors vary by species)
  • Automotive antifreeze (c=yellow-green)
  • Bacteria: some tests for pathogens in water rely on use of a black light or UV - see SWIMMING WATER TESTS for details.
  • Beverages (some, not all) or drink spills, such as the quinine in tonic water (c=blue-white)
  • Body fluids, including blood , semen, urine, both from humans and from other animals (c often yellow). For medical and forensic work we use luminol, an ultra-sensitive spray that fluoresces in the presence of blood.
  • Catsup
  • Currency: some paper money such as U.S. bills include a security strip
  • Decayed plant matter (rotten skins or fruits, e.g. banana)
  • Detergents, soaps, & bluing or softening agents & other cleaners (Mr. Clean, Irish Spring)
  • Honey
  • Olive oil
  • Party decorations designed to "glow in the dark" including face paint, hair spray, jewelry, socks, nail polish, treated colored paper, specialty balloons, specialty plastic cutlery, plates &c.
  • Plant or food material high in chlorophyll (c = blood red)
  • Salt (varies according to impurities)
  • Septic testing dye. The red or green fluorescein dye used in septic testing is usually visible to the naked eye but at low concentrations it may still be observed using a UV light.


    or see more details
  • Spices, some such as turmeric
  • Stamps, some postage

Faux UV does not show urine on cotton (C) Daniel Friedman

  • Stones, some minerals & gemstones
  • Talcum powder (common in bedrooms, bathrooms)
  • Toothpaste, brands containing tooth whitener
  • Urine from animals, including humans & pets (c=yellow)

    Watch out: as our photo at left illustrates, a "faux-UV" light such as this lamp (photo at left) sold as a mosquito killing product produces so little ultraviolet light that it does not cause urine to fluoresce. The urine-soaked cotton held in tweezers in our photo was not able to be identified by a test using this particular light source.
  • Vaseline or similar petroleum jelly products
  • "Vaseline glass" (glass containing 2% uranium dioxide by weight as a yellow ie yellowish-green coloring agent) (c=green)
  • Vitamin A & B (c=yellow)

UV light or black light information, sources, suppliers

[1] - Chemistry

[2] Several light & forensic suppliers, e.g. Doje's (see our article on checking for blood in art work by Frida Kahlo)

[3] U. Illinois Dept of Physics,

[4] Glow Paint Industries, an Australian company ( 07-5483-9181) claims to provide the world's longest list of products that glow in the dark, listing toys, party supplies, home improvement products, recreation & sport products, paints, and more.

[5]  UV WATER DISINFECTION, PORTABLE discusses using a tiny portable UV light to attempt to disinfect drinking water

and UV ULTRAVIOLET LIGHT WATER TREATMENT discusses larger capacity ultra violet light water disinfection systems selection, installation, use, maintenance, diagnosis.



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UV LIGHT BLACK LIGHT USES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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