You may have seen black lights in amusement parks, science museums, and sauna lounges. Black light may look like regular fluorescent or incandescent lamps, but they do something completely different. Turn on a switch and white clothes, teeth, and all sorts of things glow in the dark.
For example, if you have a fluorescent poster and shine it with black light in a dark room, the poster will glow. You've probably seen a piece of paper that looks blank in normal light, but spells out glowing messages in black light. The handmade stamps used in many amusement parks are invisible until you see them in black light.
In this article, we will understand what exactly happened. We'll also see why black light makes some objects glow and not others, and we'll look at some interesting black light applications.
<h1>What is "black light"?</h1>
If you turn on a black light bulb in a dark room, you can see a purple light from the bulb. What you don't see is the ultraviolet light emitted by the bulb.
Our eyes can see visible light with a spectrum ranging from red, orange, yellow, green, blue, and purple. Purple is on top of ultraviolet light, which we can't see. How sunburn and tanning work discusses UV rays and its effects on our skin. Black bulbs produce UVA light (as opposed to UVB light, which is more harmful).
The frequency of ultraviolet light is higher than that of visible light, and the human eye is invisible.
What you see glowing in black light, whether it's a fluorescent poster, an invisible handprint, or a freshly washed white t-shirt, is phosphor.
A phosphor is anything that emits visible light in response to some kind of radiation. Phosphors convert the energy of ultraviolet light from black light to visible light.
<h1>Black lights come in two forms: tubes and bulbs</h1>
The traditional black light design is just a fluorescent light with several important modifications. Fluorescent lamps emit light by passing electricity through a tube filled with an inert gas and a small amount of mercury. (For more information, see How fluorescent lamps work.) )
When excited, mercury atoms release energy in the form of photons. They emit some visible photons, but most are photons in the ultraviolet wavelength range. Because the human eye cannot see ultraviolet light, fluorescent lamps must convert this energy into visible light. They applied a layer of phosphorescence to the outside of the test tube.
A phosphor is a substance that glows or emits fluorescence when exposed to light. When a photon hits a phosphorescent atom, one of the electrons in the phosphorescent atom jumps to a higher energy level, causing the atom to vibrate and generate heat. When an electron falls back to its normal level, it releases energy in the form of another photon. This photon has less energy than the original photon because some of the energy is lost in the form of heat. In fluorescent lamps, the light emitted is in the visible spectrum — phosphorus emits white light that we can see.
The principle of black light is the same. There are actually two different types of black light, but they work in essentially the same way.
<h1>How phosphors work</h1>
A tube of black light is basically a fluorescent lamp with different kinds of phosphorus coating. This coating absorbs harmful short-wave UV-b and UV-c light and emits UV-a light (just as a phosphor in a fluorescent lamp absorbs UV light and emits visible light). The "black" glass tube itself blocks most of the visible light, so eventually only benign long-wave UV-A light, as well as some blue and purple visible light, can pass through.
The black bulb of an incandescent lamp is similar to that of a regular household bulb, but it uses a filter to absorb the light emitted by the filament after heating. It absorbs everything but infrared and UV-A light (and a little bit of visible light).
In both light designs, the emitted UV light reacts with various external phosphors in the same way that the ultraviolet light inside a fluorescent lamp reacts with a phosphor coating. External phosphors emit light as long as there is ultraviolet light.
<h1>What types of objects contain phosphors, and what are the uses of black light? </h1>
If you walk around all night with portable black lights, you'll find phosphors everywhere. In your teeth and nails, there are many natural phosphors. There is also a lot of phosphorescence in man-made materials, including TV screens, some paints, fabrics and plastics. Most fluorescent-colored things, like highlighters, contain phosphorescence, and you can find them in all the products that glow in the dark. Clubs and amusement parks use special black light paint that emits different colors. You can also buy fluorescent black light bubbles, invisible black light ink, fluorescent black light carpet, and even fluorescent black light hairspray.
Ordinary highlighters are as easy to use as "black light pens". In black light, fluorescent ink glows!
In addition to making people and fluorescent posters look cool, black light also has some practical applications. For example:
Appraisers use them to detect antique fakes. Many paints now contain phosphors that glow in black light, while most older paints do not contain phosphors.
Repairmen used them to look for invisible holes in the machines — they injected a little fluorescent dye into the fuel supply and shone it with black light. For example, they can detect invisible air conditioning leaks by adding fluorescent dyes to the refrigerant. Black lights can be used to detect counterfeit banknotes.
Law enforcement officers can use them to identify counterfeit money. The big bills of the United States and many other countries have an invisible fluorescent stripe that only appears under black light.
Recreation parks and clubs use them to identify invisible fluorescent handprints.
Forensic scientists use them to analyze crime scenes. For example, to identify fingerprints, they often apply fluorescent dyes under black light. This makes it easier to find fingerprints from the surrounding dust. Black light can also recognize semen and other naturally fluorescent body fluids.
These and many others follow a common theme—black light making invisible things visible, or separating a particular substance from everything around it. When you think about this, there are many situations where you can put this phenomenon into practice. The apps can be endless!