When you think about it, there are dozens of situations where you could put this phenomenon to work. Most of these uses, as well as dozens of others, follow a common theme - the black lights make the invisible visible or isolate one specific substance from everything around it. Black lights can also identify semen and other bodily fluids that naturally fluoresce.
This makes it easier to pick the fingerprints out from surrounding dirt. To pick out fingerprints, for example, they often dust with fluorescent dye under a black light.
Forensic scientists use them to analyze crime scenes.Amusement parks and clubs use them to identify invisible fluorescent hand stamps for readmission.The United States and many other countries include an invisible fluorescent strip in their larger bills that only shows up under a black light. Law enforcement officers can use them to identify counterfeit money.Black lights can be used to detect counterfeit bills. For example, they might detect an invisible air conditioner leak by adding fluorescent dye to the refrigerant. Repairmen use them to find invisible leaks in machinery - they inject a little fluorescent dye into the fuel supply and illuminate it with a black light.Many paints today contain phosphors that will glow under a black light, while most older paints do not contain phosphors. Appraisers use them to detect forgeries of antiques.In the next section, we'll see what kinds of objects contain phosphors, and we'll look at some interesting uses for black lights. The external phosphors glow as long as the UV light is shining on them. In both of these light designs, the emitted UV light reacts with various external phosphors in exactly the same way as the UV light inside a fluorescent lamp reacts with the phosphor coating. It absorbs everything except the infrared and UV-A light (and a little bit of visible light). An incandescent black light bulb is similar to a normal household light bulb, but it uses light filters to absorb the light from the heated filament.The "black" glass tube itself blocks most visible light, so in the end only benign long-wave UV-A light, along with some blue and violet visible light, passes through. This coating absorbs harmful shortwave UV-B and UV-C light and emits UV-A light (in the same basic way the phosphor in a fluorescent lamp absorbs UV light and emits visible light). A tube black light is a basically a fluorescent lamp with a different sort of phosphor coating.A black light bulb produces UVA light (as opposed to UVB light, which is much more harmful). How Sunburns and Sun Tans Work discusses ultraviolet light and its effects on our skin. Above violet is ultraviolet light, which we cannot see. Our eyes can see visible light in a spectrum ranging from red through orange, yellow, green, blue and violet. What you cannot see is the ultraviolet light that the bulb is also producing.
If you turn on a black light bulb in a dark room, what you can see from the bulb is a purplish glow. We'll also see why black lights make some objects glow but not others, and we'll look at some interesting black light applications.
In this article, we'll find out exactly what's going on here. Many amusement parks use hand stamps that are invisible until you view them under black light. You may have also seen pieces of paper that look blank in regular light but spell out a glowing message under a black light. For example, if you have a fluorescent poster and shine a black light on it in a dark room, the poster will glow brightly.
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