From Halloween parties and groovy dorm room posters to science museums and crime scene investigation television shows, you’re probably familiar with black light technology. When they’re turned off, black lights look just like any other fluorescent lamp – but when they’re turned on, they do something a little bit different!
If you’ve ever been around a black light, you may have noticed that anyone wearing white is glowing a little bit brighter – as well as anything that’s specifically made to work with black lights. But I’m sure you’ve wondered, “how do black lights work?” Well, the science behind UV black lights is actually pretty fascinating.
In this blog, we’ll dig into the science behind black lights, different applications for black lights, and how you can create your own black light experiments to learn more on your own.
What Does the ‘UV’ in UV Black Light Mean, Anyway?
When you turn on a black light in a dark room, the first thing you’ll probably notice is that the light isn’t black… at least not exactly. A black light bulb actually glows a blue-purplish color. But why? To understand that, we need to talk about the visible light spectrum…
The human eye is capable of seeing light that falls within a narrowly defined spectrum of wavelengths, from about 380 nanometers to about 750 nanometers, with blue and violet light being in the 380-495 range. Beyond violet light is ultraviolet light – which is invisible to the human eye.
You’re probably most familiar with the term ‘ultraviolet light’ as it pertains to the sun and its effect on your skin. But there are actually different types of ultraviolet light, including UVA, UVB, or UVC. The UV rays produced by the sun that can cause sunburn are UVB; the ultraviolet light produced by your average UV black light is UVA, and far less harmful.
When you cast your black light over a white t-shirt, an invisible hand stamp you might get at a bar, or even your teeth, you’ll notice an intensity to that trademark purple glow. What you’re seeing is the glow of phosphors – which is defined as any substance that emits visible light when exposed to some radiation (before you’re scared off by the word ‘radiation’, remember: all forms of light are considered radiation!). A phosphor is responsible for converting the invisible black light into visible light. So how does it do this?
When a light particle strikes a phosphor, it triggers an electron to jump to a higher energy level and release heat. When the electron falls back to its normal level, it releases another photon, but with less energy than the original – since some of that energy was lost as heat.
Two Types of Black Light Bulbs
There are actually two different types of black light bulbs, but both work in basically the same way:
- An incandescent black light is similar to a standard light bulb, but it includes specialized filters that absorb most of the light produced by the bulb, except for the UVA light.
- A tube black light is similar to a fluorescent bulb with a specialized phosphor coating. This coating only allows the UVA light to be emitted while absorbing the more harmful UVB and UVC light. The black coating essentially blocks most of the visible light aside from the blue-purplish glow corresponding to the UVA light.
In both designs, the answer to how these black lights work is pretty much the same: the UVA light that is emitted by the bulbs react with external phosphors, and those phosphors glow so long as they’re exposed to the UVA light.
The Many Applications for Black Lights
If you walked around all night with a portable black light, you would discover that there are phosphors all over the place. There are lots of natural phosphors, in your teeth and fingernails, among other things. There also a lot of phosphors in manmade material, including television screens and some paints, fabric, and plastics.
Most fluorescent colored things, such as highlighters, contain phosphors, and you'll find them in all glow-in-the-dark products. Clubs and amusement parks use special black light paint that glows different colors. You can also buy fluorescent black light bubbles, invisible black light ink, fluorescent black light carpet, and even fluorescent black light hair gel.
- The real CSI: Crime Scene Investigators really do use UV black lights to examine crime scenes! For example, to find fingerprints, forensic specialists will use a fluorescent dust that sticks to fingerprints. Then, they will cast a black light around the scene to reveal the fingerprints among the surrounding environment.
- Law enforcement, bank tellers, and even retail associates responsible for handling cash currency can use black light pens to confirm the authenticity of bills. In the United States, five dollar bills and above contain these fluorescent watermark strips to the left-of-center of the face of the bill. So if you ever think about paying with a fake bill, you’d better think again!
- Black lights are often used to have good old fashioned fun! From Halloween parties to neon-lit raves, black lights create a one-of-a-kind kaleidoscope of color that can be further enhanced if party-goers are properly prepared. Special fluorescent body paint and makeup can elevate a Halloween costume or festival outfit into something unforgettable. Speaking of which, remember to bring your fireworks glasses!
- Have you ever entered a baseball game or a theme park, only to have to go back to the car? You probably got a hand stamp on your way back out. Well, that’s using black light technology! Bars, clubs, concert venues, sports events, and amusement parks use fluorescent hand stamps and corresponding black lights to allow for readmission.
- Because many modern paints contain phosphors that glow under black light, an antique appraiser can use a black light to detect forgeries. The older paint found on original antiques does not contain phosphors; if it glows, it shows… that it’s not authentic!
- Air conditioning unit repair technicians can use black lights to locate otherwise invisible leaks in HVAC units. They do this by adding a small dose of fluorescent dye into the liquid coolant of the system. Then, they shine a black light on the unit and its network of vents to discover leaks in the system.
- Believe it or not, scorpions will glow under a black light. This is due to a fluorescent substance found in the cuticle of the scorpion’s exoskeleton. So, if you’re ever planning on being out in the desert at night, be sure to bring a black light to check for these potentially dangerous creatures.
- Last but not least, black lights are a great tool for studying light and color, of course! Black lights provide educators with another visually engaging experiment to teach students about the Electromagnetic Spectrum, visible light vs. invisible light, and how black lights work in general.
Discover UV Black Lights for Yourself
At Rainbow Symphony, we make it easy to learn more about how black lights work with our Hand-held 6” Black Light Fixture and UV color changing beads. Use the Hand-held Black Light to charge your color changing beads – or for a number of other black light-related activities such as illuminating black light-activated face paint at your next party!