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What Is A Black Light And What It’s Used For?

Ever been in a nightclub or maybe an indoor mini golf center and wondered how they get that glowy effect from fluorescent paint in dark rooms?

That’s down to black light, a type of ultra-violet light that isn’t normally visible to the naked eye.

You might’ve heard of black lights before, as they’re sometimes mentioned in cop dramas, too – they have many uses.

A black light emits a short wavelength light above the visible spectrum with high frequency. This is absorbed by certain fluorescent molecules found in certain paints, some bodily fluids, and other materials, which causes these to glow.

In this guide, I’ll take you through everything you could want to know about black lights, including:

  • What it is, in more detail
  • Whether UV lights are the same as black lights
  • Uses for black lights
  • Whether LEDs can be used to produce black light

What Is Black Light?

documents under black light

To understand black light, you need to realize that ‘light’ energy does not just consist of the light we can perceive.

There is a much broader spectrum of what is ultimately electromagnetic radiation – electromagnetic waves of energy.

This ranges from low-frequency energy – gamma rays and x-rays – to high-frequency radio waves.

Visible light sits on that spectrum, with a wavelength between 400 and 780 nanometers.

Directly above that is infrared light, and directly below it is ultraviolet light – and part of that ultraviolet range is a black light.

It’s called black light simply because it is light you can’t see.

There’s a lot of this energy that you can’t see, including microwaves, x-rays, and so on – but black light refers specifically to the light just below visible light on the spectrum, from around 320 to 400 nanometers.

Now, if you have a black light flashlight or tube light, you can see some light when you switch it on – it’ll have a purple glow.

That’s just the energy at the bottom end of the visible spectrum. So most of the light being emitted will be invisible black light.

Is Black Light A Health Hazard?

As soon as you start talking about words like “radiation” or mentioning “ultraviolet” or “UV” light, there are obviously going to be concerns about whether black light is a health hazard.

Thankfully, there are no major concerns about black light – it is generally considered safe to use.

The ultraviolet light of black light is on the higher wavelength side of ultraviolet light and is classified as UVA.

UVA in high concentrations has been linked to skin aging, but not in the typical concentration given out by any manufactured black light bulb.

You’ll be exposed to more UVA standing outdoors in the sunshine than with a black light.

However, it’s not recommended to stare at a black light anytime.

While you’re not going to be exposed to harmful radiation, you could strain your eyes without realizing it.

If you’re somewhere with a black light or using one, try not to look directly into it.

Generally, avoid being somewhere where there are a lot of black light bulbs for a prolonged period.

A visit to a typical nightclub using black lights won’t be an issue, though, as you’d only spend a couple of hours there. The combined black lights shouldn’t be powerful enough to cause harm.

Is UV Light The Same As Black Light?

runners participate in blacklight run

So we’ve established that black light is on the ultraviolet part of the light spectrum, so does that mean it’s the same as UV light?

Yes and no.

Black light is a type of UV light, and that’s true. However, the light that it emits is ultraviolet.

But generally, when we talk about “UV light,” we’re talking about a specific type of light with a shorter wavelength – typically 280 to 320 nanometers.

On the other hand black light is ranging between 320 and 400 nanometers.

UV light is the type of light used for purifying water and other germicidal purposes, including sterilizing surfaces used for food prep.

UV light emits the UVB type of light, which tans the skin, so if you were to visit a tanning salon, you’d be using UV lights, not black light.

Of course, this also makes UV light much more dangerous than black light since continued exposure is harmful to your skin and can lead to burning and even skin cancer in the long term.

There are also UV lights that emit UVC energy, which has an even shorter wavelength again.

These are not produced as widely and have very specialist uses for killing germs. However, they’re also more dangerous than UVB light and should be used with extreme care.

We aren’t used to UVC exposure because this energy is usually absorbed by the ozone layer in the atmosphere when it reaches us from the sun.

In short – they aren’t the same and make sure you’re buying a black light with a wavelength between 320 and 400 nanometers if you want to stay safe.

What Is Black Light Used For?

Black lights have a lot of different uses, including some that are fun and some that are more useful.

Let’s start with the more practical applications.


getting evidence under black light

Black lights are used a lot by forensics experts and criminologists because three of the primary bodily fluids – blood, urine, and semen – all glow under black light, and it can make finding traces of these fluids much easier.

Crime scenes are often large and complex to search. Also, individual items considered evidence may have been given a cursory wipe down but could leave residue behind that isn’t visible to the naked eye.

A quick scan of a room or an object with a black light can be very revealing. It could enable testing to be done to identify suspects or help work out the timeline of an event.


Black light illuminating a spot where a male cat keeps spraying pee

A use that’s more practical for most people would be cleaning.

Because black lights show up these common fluids, it can make cleaning an area a breeze.

Specifically, black light flashlights (Amazon) are really handy for owners of cats and some other animals that may urinate in places they aren’t supposed to.

Cats will usually use their litter tray as their toilet, but if they are old, unwell, or just anxious, they may start spraying urine elsewhere in your home.

Cat urine is particularly pungent but is annoyingly invisible once it soaks into a fabric.

So if your cat has urinated somewhere around your home, finding the offending spot to give it a deep clean and eliminate the smell can be tricky – but a black light makes it much easier.

Pet owners and anyone particular about cleanliness may like to carry a black light flashlight with them.

Anyone who visits hotels regularly could use one to check whether their room has been properly cleaned.

Counterfeit Checking

Check the authenticity of money with black light

Most modern bank notes will contain hidden elements that only appear in black light. These are harder to recreate and therefore help stem counterfeit bank notes problems.

If you’ve ever handed a banknote over to a teller in a store and they’ve inspected it, they’re probably using a black light device to check for the markings.

Some stores will have a policy to check any high-value note to ensure it is legit.

If you own your own business or you deal with a lot of cash for other reasons, a black light might be a useful tool to make sure you’re not getting dumped with counterfeit notes, which are ultimately worthless.


curing black light dentist

There are some medical uses for black light.

While stronger UV lights will be used for disinfection, a black light can help identify certain skin conditions, such as psoriasis or types of acne.

While these may be visible under normal light, there are different causes for skin problems. A black light can help narrow down the diagnosis, which means the proper treatment can be used.


It’s not just bodily fluids that glow under a black light – most car fluids will too.

So if your car has a leak, you can use a black light to find the source, and it should be much easier to repair it.

Discreet Entry Stamps

Many bars, theme parks, and other locations will use hand stamps to show who has paid for an entry.

Many choose to use ink that isn’t visible to the naked eye.

This benefits the entrant, who doesn’t have an unsightly mark on their hand, but it also helps the business since it can’t be easily faked by someone looking to gain entry.

Equip the doorman with a black light, and they can easily see who is welcome to enter and who still needs to pay.

Cool Things You Can Use Black Light For

fluorescent make up under black light

You can use black light for some fun things, and while maybe not the most useful, can add a fresh new take to regular activities.


Many entertainment venues are set up as dark spaces, using fluorescent paints combined with a black light to create a glowing neon effect.

It can be popular in nightclubs, but an indoor mini golf course is another common location.

Using darkened spaces, neon-style paints, brightly-colored balls, and club heads make for a unique and fun challenge.

Make sure the hole is also painted. Otherwise, putting it will be very difficult!

If you visit a nightclub with glowing decorations, try ordering a drink with tonic water, as this will often glow too.

Don’t worry; it’s still safe!


Search online for “black light clothing,” and you’ll find loads of options for t-shirts, dresses, accessories, and more styled to glow in black light conditions.

If heading to a black light party, ensure you’ve picked the right wardrobe first.

But if you’re on a budget, wear white – most white cotton materials will have at least a gentle glow under a black light.


Complete your look with fluorescent cosmetics, including traditional makeup items or face paints.

You can get creative and end up with funky designs when you enter a black-lit space.

Why Things Glow Under Black Light?

blood under black light

The substances that cause items to glow under a black light are phosphors.

Phosphors absorb the energy of black light and then emit their own light in the visible spectrum.

Anything marketed as ‘glow-in-the-dark’ will contain phosphors, as will anything marked as ‘fluorescent.’

But they are also found in other substances, including the aforementioned bodily fluids, various vitamins, and other chemicals, including some laundry detergents – which is why white clothing will often glow.

Essentially, anything which glows under a black light contains phosphors of some kind.

Can LEDs Emit Black Light?

Typically, black light has been created using fluorescent tube lights. However, some incandescent black lights have also been designed to emit black light.

But this is the modern world – can’t we get LEDs to create black light?

Yes, we can – but they must be specifically designed for the job. For example, you can’t set a normal LED strip light to a black light setting.

It’s pretty easy to find and include special light bars or LED strip lights that emit black light.

Just like regular visible lighting, LEDs will be more energy-efficient and longer-lasting than their incandescent or fluorescent counterparts.

Expect a fluorescent light bar to last around 7,000 hours and a similar LED one to last 25,000 hours.

Final Words

Black lights are cool, but you’ll need to have a specific purpose in mind to buy one. These aren’t the lights you would typically buy to illuminate a space.

There are a lot of potential uses for one, though, so consider picking one up if any of those ideas above sound useful to you.

They’re definitely a handy tool for any cat owner!

Have you bought a black light before, and did you find any other uses?