What Does A Black Light Show On Carpet?

Black lights are probably best known for accompanying glowing hippie posters and being the main lighting for rave parties, but they have many practical uses as well. Something black lights are commonly used for is detecting stains and spills that cannot be seen under regular light. But exactly what kinds of substances will appear? We've done the research to bring you the answer.

If you are wondering what kinds of stains and substances you can check for with a black light, we have outlined these for you. Things that commonly show up under a black light are:

  • Bodily fluids
  • Laundry whitening products
  • Quinine (tonic water)
  • Lemon juice
  • Toothpaste with whiteners
  • Vitamins
  • Antifreeze
  • Petroleum jelly
  • Mold
  • Some foods (turmeric, certain oils, honey, ketchup)

Using a black light is a useful way to see what kinds of substances may be lingering in your carpet even after cleaning it or to check if a spill was cleaned properly and thoroughly. This post will help you get your carpet as clean as possible!

Worker's Hands Rolling Carpet At Home and UVC G23 fluorescent bulb, What Does A Black Light Show On Carpet

What Is A Black Light, Anyway?

A “black light” is a type of light bulb that emits ultraviolet (UV) light. UV light is outside the visible range for humans, so items that can be seen under UV light usually cannot be seen by humans in normal light.

UV light excites certain particles and causes them to fluoresce, which produces the glow. The glow is best seen in the darkness, so turn off all the lights in the room to get the best light conditions for stain detection. You will want to use a light that specifies it is an ultraviolet light to get the correct effect. 

Check out this UV flashlight black light on Amazon.

What Substances Glow Under A Black Light?

Substances glow under a black light, What Does A Black Light Show On Carpet?

Now let's cover an extensive list of substances that glow under a black light. Some may even surprise you! Discovering these otherwise hidden spills and stains can significantly help your cleaning process. With the help of a black light, your house may be cleaner than it ever has been before.

Bodily Fluids 

This includes blood, saliva, urine, and semen. And this is not limited to human bodily fluids – animal fluids will glow under a black light as well. Many people do this when they are cleaning up after a dog or cat who has been marking their territory inside the house.

There is one exception to this – blood. Blood by itself will not glow under a black light, but it does react with a chemical called luminol which will cause it to glow. Forensics investigators commonly spray luminol around crime scenes, so they are able to use a black light to detect blood.

Does your carpet have some funky smells coming from it? You might like our post, Carpet Smells Like Stinky Feet? Here’s What To Do.

Laundry Detergents 

Some laundry detergents and other laundry products contain whitening agents in them. These whitening agents fluoresce under a black light, which can cause light-colored clothing to glow blue because of the residue left by the detergent. If some liquid detergent is spilled onto a carpet, a black light could be used to check where the spill is and whether it was cleaned thoroughly.


Quinine is commonly found in tonic water and other beverages. It is also a medication used to treat malaria. Quinine has chemical properties that cause it to fluoresce light blue under UV light. So, you can use a black light to make your gin & tonic glow blue – and to find the spills after the party!

Lemon Juice 

Did someone spill a glass of lemonade or a bottle of lemon juice in your house? Use a black light to see where the spill is and make sure it all gets cleaned up. Lemon juice will glow a light bluish-green under a black light.

Toothpaste With Whiteners

Just like laundry detergents, whitening toothpaste and whitening products contain compounds that glow a light blue when under a black light. If the bathroom is your next cleaning project, check out our post, How To Wash Bathroom Rugs [Machine And Hand Washing Explored].


Certain vitamins, namely vitamin A and B (niacin, thiamine, riboflavin) will glow bright yellow under a black light. This is useful if vitamin capsules or crushed tablets are spilled onto the carpet. In homes with pets or small children, it is very important to make sure these things are cleaned up because they can be dangerous if ingested.


Automotive antifreeze used in car radiators has fluorescing agents included in it purposely – you can even see the “glow” in regular light. Antifreeze is toxic to people and pets, so if there is an antifreeze spill in the home or garage, a black light can be used to make sure the area is cleaned up and safe.

Petroleum Jelly 

A common household and personal care product, petroleum jelly, contains particles that phosphoresce in UV light. So when under a black light, any petroleum jelly smears or stains will glow bright blue.

Does Vinegar Show Up Under Black Lights?

White vinegar on bottle

Vinegar will not glow under a black light by itself, but if combined with a crushed up Vitamin B-12 tablet, it will glow a bright yellow.

Does Mold Show Up Under Black Lights?

Lamp ultra-violet to kill bacteria in air

Yes, it does. If you shine a UV black light over an area with unseen mold, it will glow a bright yellow-green. This is a great way to check for mold in places where there have been leaks or moisture buildup. The black light should be held close to the suspected area to achieve the correct angle. 

Check out this LED black light on Amazon.

What Color Glows Under A Black Light?

Fluorescent multicolored hand print on black background

Most of the time, anything that is neon or fluorescent colored will glow under a black light. Neon green, pink, yellow, orange, blue, and purple are very common. Most white objects, especially clothing, will also glow a bluish tint under a black light.

Can You Turn Your Phone Into A Black Light?

Silhouette of male hand lit with blue and red neon lights holding bezel-less smartphone on black background

There are hacks to turn your phone’s flashlight into an approximation of a black light, but it will not work quite the same as a “real” black light. However, you can try this hack with some clear tape and blue & purple markers. Follow along with this tutorial to turn your phone into a black light:

In Closing

So if your carpet is in need of some cleaning, or if you know that a specific substance has been spilled on it, a black light can help you detect stains, residues, and unwanted substances. If you want to thoroughly clean and sanitize your carpet, a black light is one tool you may want to add to your cleaning products!

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