Uses for UV flashlights
A post about UV lights often generates questions about why one would want to have a UV light. Here are some of the things people do with UV lights, gleaned from past BLF threads and internet searching.
Cheaper lights found on Ebay and other places on the internet (generally less than $20) commonly use inexpensive LEDs with wavelengths of 380nm or higher. While technically UV, the brightness of the fluorescence that we see is directly related to wavelength, with shorter wavelengths and brighter LEDs producing more fluorescence. These days powerful LEDs are available at 365nm wavelengths and these are the best LEDs to look for in flashlights if you want to see bright fluorescence. These LEDs emit in the UVA and UVB wavelengths. Powerful light with shorter wavelengths exist in shorter wavelengths, such as the UVC at 254nm. These light produce the brightest fluorescence in most materials but so far LEDs in these wavelengths are much lower power than 365nm so have yet to be useful in flashlights. Specialized lights (expensive) are made for mineral collectors.
1) Checking validity of currency and other documents. Many currencies now incorporate fibers and stripe that fluoresce under UV exposure. These bills are a handy test for how well a UV light is performing. Cheaper lights with wavelengths of 380-400nm will show dim or even no fluorescence. High quality lights of 365nm show bright fluorescence. TSA uses a UV fluorescent light to check the validity of your drivers license when you go through security at the airport. Certain inks can fluoresce and be used to check documents for forgeries. Forgeries of bank notes, standard checks and travellers’ checks are mainly printed on inferior bleached paper or photocopied. Forgeries will glow under UV light and bona fides will be completely dull. Many newer credit cards have an invisible imprint on the front. American Express uses “AMEX”. If no imprint, the card is a forgery. Alterations of legal documents such as careful erasure or ink eradication and altering paper textures are detectable with UV light. Some products are now imprinted with seals that fluoresce in UV as a protection against fakes.
2) Crowd control. Bouncers use UV lights to check for hand stamps at events.
3) Leak testing. Ethylene glycol used in your radiator or other cooling systems has an additive that fluoresces in UV light. Mechanics can use this to locate a leak in the cooling system. For other systems like oil in your car or refrigerant in your air conditioner you can add a fluorescent tag to the oil to help locate leaks. House inspectors can use this to identify leaks from various systems within the house.
4) Finding urine stains or animal tracks. Urine contains proteins that fluoresce under UV exposure. If you are smelling a urine smell from your pet but can’t find where it is coming from a UV light may help you find it. Animals like mice tend to mark their territory and pathways with urine. You may be able to find where the mice are entering your house using a good UV light. Biologists can use UV lights to track animals. Recent studies have correlated the fluorescence of urine at certain wavelengths to the development of cancer. Not something you can check with your flashlight, see a doctor instead. Rodent hair glows blue white and is easily identifed on sacks or intermixed with grain.
5) Gem and Mineral collecting. Many minerals fluoresce in UVC (254nm) but fewer do in UVB (365nm). However the power of modern 365nm LEDs has revealed minerals formerly thought to not fluoresce that actually do. There is a fairly large community of fluorescent mineral collectors and the availability of powerful 365nm flashlights has been a boon to this group. Some gem materials fluoresce whereas fakes don’t. If you are collecting jade, this might be for you.
6) Amber collecting. Amber (the hardened sap of ancient trees) fluoresces nicely, again due to certain organic compounds. Some beaches are great places to look for amber.
7) Crime scene investigation. As we have seen, certain body fluids fluoresce due to the presence of proteins. A number of UV flashlights are marketed to the forensics industry, primarily at high prices. This property is also used by some people to investigate hotel rooms to look for, uh, fluid stains and how well they have been cleaned. Personally I’d rather not know. You should take a UV light into your bathroom some time if you want to see a crime scene.
8) Antique collecting. Vaseline glass and some other types of glass fluoresce brightly due to additives used to color the glass (uranium in the case of vaseline glass giving a bright green fluorescence). Having a compact and bright UV flashlight is handy when shopping for this type of glass. Some types of colorings used in paintings also fluoresce and can be used to verify the age or validity of painting by a knowledgable collector. You can use a UV flashlight to collect sea glass on beaches.
9) Scorpion hunting. The horny carapace of some scorpions fluoresces brightly under 365nm UV. If you want to kill the ones in your back yard, get a good UV flashlight. Some people actually collect them.
10) Photography. Bright UV light sources have been used in the last few years to investigate the invisible world that humans don’t see but insects and a few other animals do. Many flowers have patterns that are visible only in the UV.
11) Mushroom hunting. Many mushrooms fluoresce brightly.
12) Ghost crab chasing. On beaches south of NC in the US a UV light shows these little crabs all over the beach. Fun for kids.
13) Arson detection. In arson detection, accelerants’ fluorescent glow is greater when exposed longer to heat. Their evidence is not always visible as they are absorbed by the fire but UV light can expose them. Volatile hydrocarbons such as gasoline, grease, paints and others fluoresce when exposed to UV, and can detect fragments of incendiary devices. Ambient light must be minimized for use of UV light at a fire scene.
14) Tonic water glows under UV illumination. So do the spots on bananas. Amaze your friends!
Use your imagination…
Safety notice: UV light is dangerous for your eyes. Do not look into the beam and be sure to wear protective glasses when using a strong UV flashlight. Reflections off shiny surfaces can direct the beam into your eyes by mistake. You won’t know you have damaged your eyes until you get a case of “snow blindness” caused by the UV burning your retina.
