Blacklights Are Used in Forensics, Security, and Pest Control

by AngelaJohnson

Blacklights are used by law enforcement officers, forensic scientists, and for commercial purposes (as well as entertainment).

Ultraviolet radiation (fluorescence) cannot be seen by the human eye, but black light can make it visible. Blacklight blue or "BLB" lights have a dark blue filter coating on the tube, which has a dim violet glow when switched on. The blacklight tube filters out most visible light, so that fluorescence glows can be seen.

There are other types of blacklight tubes called "BL," but they have no filter coating and have a brighter blue color when turned on. These are usually used in "bug zapper" insect traps.

There are also incandescent light bulbs (the kind you screw into a light socket) called blacklight. Do NOT buy these if you want to use true blacklight. These inexpensive incandescent bulbs become extremely hot during use, don't filter out much external light, and don't last very long.

What Materials Glow Under a Blacklight?

Common Items That Glow Under Black Light:

U.S. $20 bill under blacklight

~ U.S. $20 Dollar Bill - The modern $20 bill has a security strip near one edge that glows under a blacklight. Most higher denomination bills of many countries contain a similar security strip.

~ White Paper – Modern paper made after contains fluorescent chemicals to make them appear brighter.

~ Body Fluids – Urine, blood, and semen all glow under a blacklight.

~ Laundry Detergents – Some whiteners in detergent make your clothing somewhat fluorescent, even after rinsing.

~ Tonic Water – Tonic water contains quinine, which glows under a blacklight.

~ Antifreeze – Manufacturers include fluorescent additives to antifreeze to help with finding leaks and accident investigations.

~ Tooth Whiteners – Whiteners contain ingredients to keep teeth from appearing yellow, that glow under blacklight.

~ Petroleum Jelly – Petroleum jelly glows under a blacklight.

~ Some Vitamins – Vitamin A and the B vitamins are fluorescent. Dissolve the vitamins in vinegar to make them glow under blacklight.

~ Some Minerals and Gems – Gypsum, quartz, opal, ruby, agate and amber are some of the minerals that are fluorescent.


Photo from Wikipedia

Blacklights Are Used for Crime Investigating and Fraud

The T206 Honus Wagner baseball cardThis photo is of a valuable T206 Honus Wagner baseball card.

Collectors and appraisers use blacklights to detect forgeries of paper collectibles, antiques, oil paintings and other valuables. Many modern inks, paints and dyes can be made to look old and authentic under visible light. However, blacklight can bring out differences because newer substances usually include synthetic materials.

People often use invisible ink to secretly mark valuable objects in case of theft or owner dispute. A blacklight can reveal the mark. If a visible mark was used, someone could scratch if off or mark something over it, but a thief wouldn't notice an invisible mark.

Law enforcement officers use blacklights to identify counterfeit money. Larger denomination bills from the U.S. and many other countries include a fluorescent strip that can only be seen under a blacklight. Similar security features are often applied to identification and credit cards.

They also use blacklights to reconstruct automobile accidents. Antifreeze contains fluorescent additives so a blacklight can pick up antifreeze splashes that occurred during the accident.

Forensic scientists use blacklights to analyze crime scenes. They often dust for fingerprints with fluorescent dye, making it easier to see fingerprints amid dirt or other substances. They also use blacklights at crime scenes to find blood, urine, or semen (all which fluoresce).

Photo from Wikipedia 

Large Ultraviolet Blacklight Flashlight

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This large rugged, machined aluminum UV flashlight with 51 UV LEDs allows you to cover a much bigger area without losing the intensity of the UV light. The applications is perfect for inspection applications, security control, rodent contamination, hotel room inspection, and much more.  Makes semen stains and other bodily fluids fluoresce! Perfect for outside use such as hunting scorpions and minerals! Water and shock resistant! Perfect for leak detection (when used with UV dye)!  UV protective glasses are recommended. Do not look into this device while operating nor shine in any person's eyes. 

Blacklights Have Many Commercial Uses

blacklight flashlight~ Fluorescing fluids applied to metal structures will show cracks and other weaknesses when illuminated with a blacklight flashlight .

~ Since body fluids fluoresce under blacklight, hotel management can inspect hotel sheets to make sure they’ve been changed. Blacklight can also determine if public restrooms are being cleaned properly.

~ You can use a blacklight to check on the cleanliness of your hotel room, look for bedbugs or evidence of rodents..

~ UV leak detection systems using blacklight can aid repairmen locate oil leaks, air and conditioning system leaks, and other leaks in machinery.

~ Animal urine will fluoresce under UV. Blacklight helps locate cat urine in carpets or determine if there are rodents in the house.

~ Store merchants and sellers can put an invisible ink mark on merchandise and use a blacklight to make sure a customer is returning the original item.

NOTE: UV protective glasses are recommended for use with blacklight. Just as you wouldn’t look into the sun or directly at light bulbs, don’t look at blacklight. 

 Image of a blacklight flashlight from Amazon.

Invisible Blacklight Ink to Mark Valuables and Write Secret Messages

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Use a Blacklight For Pest Control

Tomato hornworms can be tough to find because they blend in so well with the plant leaves. Horn

worms can eat a plant almost overnight, though. To save your tomato plants, go out at night and shine a blacklight on them and they’ll glow.

Other animals that fluoresce under a blacklight are scorpions, crayfish, centipedes, and millipedes.

If you think you have roaches, mice, bed bugs, or other infestations, a blacklight will help you find their body fluids so you can know where to set traps. You’ll have to pay particular attention to the glowing areas, though, because some household cleaners also glow under blacklight.

If your cat or dog is urinating in your house, use a blacklight to find the spots so you can clean them.

And just for fun, Black-eyed Susan flowers have yellow petals, but under black light their markings give them a bull’s eye type design. (I haven’t seen this, but I read about it).

NOTE: When you use blacklight, you must be in the DARK, so this method won't work if you can't turn off outdoor lighting.

Photo by Justin on flickr 

Tomato Hornworm

Tomato Hornworm

Test Antiques and Collectibles with a Blacklight

vaseline glass under blacklightAlthough using a blacklight may not be the final say on whether an antique or collectible is authentic, it's a good place to start. 

~ Determine if glassware has been reproduced.

Green Depression glass and Vaseline glass glow under a blacklight because the glass contains uranium oxide. I've seen both vaseline and green depression glass glow.

Other collectible glassware may fluoresce, too, but you'll need to do some research on whatever glassware you're collecting.  

~ Detect repairs and paint touch-ups.

Repairs on porcelain may be so good you can't see it just by looking at the piece.  But if it's been repaired, the glue will fluoresce.  And if an item has been touched up or repainted, modern paint will also glow under blacklight. 

~ Determine if old paper products are actually modern. 

Old books, photos, postcards and other paper products made before 1940 rarely glow under a blacklight, but modern papers with bleaches and dyes will. Using a blacklight will help eliminate fakes and reproductions, but if you're about to buy a high-priced rare paper product, have it examined by an expert who will have additional ways to test its authenticity. 

~ Date old fabric and determine if it's been repaired.

Modern fibers like rayon and polyester fluoresce under a black light. This you know if a quilt, old doll, vintage clothing, and other collectible textiles are modern.  A blacklight will also bring out repairs by showing you modern thread or bits of new material incorporated into the old item. 

Be aware that if an older textile has been cleaned with modern laundry detergents, this many make the item glow, too.  Many modern detergents have additives that glow under a blacklight.

photo from flickr creative commons

Pocket Flashlight Description

Compact and lightweight, the Streamlight Stylus is a portable penlight with a high-intensity LED that lasts up to 100,000 hours. It is designed for comfort and durability with a waterproof, machined aluminum case and a pocket clip for easy portability. Featuring momentary-blink and constant-on switches, the Stylus Penlight has different-colored LEDs available (each sold separately), so you can use it in a variety of applications at home or at work.

Updated: 04/01/2019, AngelaJohnson
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Have You Ever Used a Blacklight?

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AngelaJohnson on 01/30/2015

frankbeswick - the only drawback to using blacklight is that you have to use it in the dark. But it's still a great detection tool.

frankbeswick on 01/30/2015

Well, Angela, when I studied integrated pest management in my Horticulture course I was not told about the use of blacklights for pest detection. So what you have said is information new and useful to me. Crayfish are a nuisance in Britain,so a means of detecting them is a valuable tool in the pest control arsenal.

DerdriuMarriner on 01/29/2015

burntchestnut, Oh, my, quinine glows under a blacklight! I am partial sometimes to tonic water -- fortunately in delicate enough quantities that there should be no buildup in my tissues for a telltale blacklight to discern. :-0

ologsinquito on 01/23/2015

What a great article. I knew these lights are used for pet urine on a carpet. Otherwise, there would be no way to find it, and no way to get rid of the odor.

WriterArtist on 01/20/2015

That is so interesting to know. I did not know that black light was so important. Its varied usage in forensics, crime and even pest control leaves me wondering what are the other uses that we still do not know yet. Now that's what I call an amazing thing. I found this article quite educational.

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