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why do things glow under a blacklight

This woman is wearing make-up that glows under a black light. The colors would not show up under ordinary lighting conditions. Piotr Stryjewski / Getty Images
There are a lot of everyday materials that fluoresce or glow when placed under a black light. A black light gives off highly energeticP. You can t see this part of the spectrum, which is how black lights got their name. Fluorescent substances absorb the ultraviolet light and then re-emit it almost instantaneously. Some energy gets lost in the process, so the emitted light has a longer wavelength than the absorbed radiation, which makes this light visible and causes the material to appear to glow. Fluorescent molecules tend to have rigid structures andP. Here are 17 examples of common everyday materials that contain fluorescent molecules so they glow under a black light.

At the end, I have a list of all the materials listed, plus additional things people report as glowing. Santos, The colors of light that the human eye is able to see range roughly from red to blue in color. Blue light has a higher frequency than red light. The light which has frequency just lower than red light is called "infra-red", and the light which has frequency just higher than blue light is called "ultra-violet". Both infra-red and ultra violet-light are beyond our eyes' range for efficiently detecting, however they are still very important. Infra-red light is often used to warm things (like heat lamps over food in restaurants), and ultra-violet light is the subject of your question.

A "black light" is just a light bulb designed to emit ultra-violet light. The reason these are called "black" is that if you look at the actual bulb it does not seem very bright (sort of a dim violet color), and if you put a black light in a dark room it really does not brighten it very much. the room remains almost black. These bulbs do emit lots of light however, its just that we cant see it. Some materials have the special property that they absorb ultra-violet light and then re-emit the light at lower frequencies that our eyes CAN see. This is called "fluorescence". These materials are sometimes found on our t-shirts, jackets or shoes, and when we walk near a black-light they will seem to "glow" since they are translating the invisible ultra-violet light into easy to see colors, most often white.

If you have a black-light handy, why dont you do the following experiment: Try putting different kinds of materials near it and make a list of which ones glow brightest and what color you see. Once you do this, tell us your results (use this web page again) and will post them for everyone in the world to see. Some of the materials you might try are different foods and drinks, plastics, bleach (ask your mom or dad first), dirt. whatever you can think of. Let us know how it works, MS (published on 10/22/2007)

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