Ultravolet Light
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Light can be described by the length of its sine wave, just like radio waves can. Typically the 
human eye can see from 380 to 750 nanometers. Lots of other animals, reptiles, and insects can see perfectly well the colors that are beyond the range that humans can.
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Red is on the long wave part of the spectrum at approx 725 nm. And blue or purple is at the shorter wave length end of the spectrum around 400 nm.
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Beyond the blue or purple is the light which we cannot see (but lots of insects and animals can see). It is called ultraviolet light or UV. Some minerals have an interesting property: When they are illuminated with ultraviolet light (which is invisible to the human eye), they emit light in the part of the spectrum which is visible to humans. This is called fluorescence. If the visible light continues even after the UV light is shut off, this is known as phosphorescence.
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The cheap black lights that you can buy at Wal-Mart emit longwave UV light which has a wavelength of around 400 - 315 nm. This is also called UV-A. A good commercial light will typically emit light at 368 nm.
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You have to spend more to get a light which shines as shortwave UV about 280 - 100 nm. This is known as UV-C. It is germicidal and hazardous to your eyes. You need to wear glasses which stop the UV-C if you are going to be around it. 254 nm is the common wavelength of commercial lamps.
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Between LW and SW UV is UV-B or medium wave UV light. Many commercially available medium wave lights shine at 312 nm. It is so neat to look at minerals which fluoresce in 3 distinctly different colors when illuminated by each of the above colors of UV light. I now own two shortwave UV lamps made by Don Newsome of UV Systems. LINK: http://www.uvsystems.com/
I also have two Way Too Cool lamps made by William Gardner. LINK: http://www.fluorescents.com/uv.html
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The build quality is excellent from both manufacturers. I would recommend both. It has taken me about a year to come to this conclusion, but after using the lights from both companies under many different circumstances, I clearly think you get more for your money with the Way Too Cool lamps.
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