Blacklights Are Used in Forensics, Security, and Pest Control

~ 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

This 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 

~ 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..

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 

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.