What is a black light exactly?

I've always wondered what a black light really is, but until class yesterday, I never really thought about researching them. I remember watching "Room Raiders" on MTV in Middle school and high school, and them using black lights to detect "unseen stains" and then at concerts and performances, they were always a hit, because they made everyone glow... but I never knew what exactly they were.

It's called a black light due to the fact that it releases very little light that the human eye can see. So it's wavelengths start at the far end of the high-energy visible light range (HEV).

I learned that we see these wavelengths as deep blues and violets, and then the wavelength become so short and scattered that the human eye can no longer perceive them. This is when they become ultra-violet radiation.

It turns out too, that the black light is very similar to the colored lights we were using in class, in that it's a fluorescent light tube, with paint on the inside, restricting the light from shining out.

I also figured out, that based on the different wavelengths of the blacklight, they are used for different purposes, before I thought the blacklights used in concerts, and on "Room Raiders" were all the same light, with the same wavelength and frequency. However thy are not, as demonstrated by this chart....

Though all black lights emit UV rays, they can be used for different purposes depending on their wavelengths within the UV range. Wavelengths are measured in nanometers (one billionth of a meter), with the UV spectrum generally falling between 100 and 380 nanometers (nm). This spectrum is divided into three categories:

UV-A	380nm - 315nm	Long Wave (black lights, concerts, entertainment)
UV-B	314nm - 280nm	Medium Wave (forensic applications)
UV-C	279nm - 200nm	Short Wave (germicidal, sterilization)

From: http://www.wisegeek.com/what-is-a-black-light.htm

There are also tattoos now, which use ink that glows fluorescently under the light of a black light, but are very light and/or near impossible to see otherwise....

I think that's quite cool... but at the same time, I wonder what the chemical properties are of the ink...