Interesting : What is the difference between a black light and a normal light bulb?

What is the difference between a black light and a normal light bulb?

Black lights come in two varieties -- fluorescent tube and incandescent bulb. Each type works slightly differently, but both are very similar to their normal white-light cousins. Fluorescent tube lights are glass tubes that contain a near-vacuum with a little mercury vapor. When electricity is passed through the tube and reacts with the mercury, it creates light. The mercury atoms emit energy in the form of light photons. These photos are mostly in the ultraviolet (UV) range of the light spectrum. We can't see this light, so a white phosphor coating on the light tube is used to convert the UV energy into visible light. A black light works the same way, except the tube is made of dark blue glass, and it is coated with a special phosphor that blocks visible light and harmful UV rays. Only the rays of UV light that are harmless pass through, along with a little bit of blue and violet visible light, resulting in the distinctive glow of a black light. The incandescent bulb type of black light also uses dark-blue glass, but a filter inside the bulb absorbs visible light and lets harmless UV light through. This is because of the differences in how incandescent lights and fluorescent lights work. Bulb black lights are generally less powerful than tube black lights. When you see something glow under a black light, that item contains phosphors, which glow in UV light. Teeth, fingernails, and some bodily fluids naturally contain phosphors, and this makes black lights useful in criminal forensics. Many laundry detergents contain phosphors to make white clothes look brighter, which explains why white T-shirts may glow at a rave. Fluorescent and glow-in-the-dark paints, inks, fabrics, plastics, and makeup all contain phosphors to give them a nifty glow. There's even a fluorescent security thread in paper currency from the U.S. and other countries that shows up under black light and acts as a deterrent to counterfeiting.