A black light may be formed by simply using Wood's glass instead of clear glass as the envelope for a common incandescent bulb.

I found my Blacklight in a thrift shop ,The bulb is interchangeable with an ordinary one .but it is not "black" at all. so I'm sure painting it black is not the way to go. I use my blacklight for looking at my drawings in which I use Glo-pens, Fleuro ink and sparkle pens, either in all the drawing or to highlight certain lines. Most of my art is linear and geometrical or even tesselations (repeat patterns). It's amazing the difference this makes to the impact of the work. Try it you will be amazed. Don't forget to use in a darkened room. Good luck. As this is Instructables why not give it a go.

Ummm fluorescent blacklights are easy to find and cheap, you could get some replacement bulbs and just use a normal fluorescent light holder, that may save you a bit of money...

Assuming you don't want to string together some UV LEDs, you can look for one of these Compact Fluorescent Black Light Bulbs, which are especially nice cause they'll go in any normal light socket. Especially check out party stores just after Halloween; I picked up several at 50% off. Avoid the purple-glass incandescent lights; while they're cheap, they don't emit very much UV.

Plug for Phenoptix, because he supplied my UV LEDs and is sponsoring the contest.

what a blacklight emits is: lamp emitting electromagnetic radiation

Just FYI: Electromagnetic radiation is also known as "light" (including non visible spectrum).

Black lights, as we know them, are "near UV" light sources (they produce "long wave" UVA's) . The reason they have that purple/blue is because of the glass (wood's glass IIRC) that blocks all light above 400nm.

The tube by itself is no different from your typical fluorescent tube except it only use one (I think sometimes two) phosphors and the glass. The ballast is identical, as is the connectors. The only difference is the bulb itself.

As for making it... Not sure how to DIY a fluorescent tube - but it seems out of reach to be cost effective. It'd be cheaper to buy ;)

so in order to make a black light i (the stupid half of me) would think to dip a lightbulb in black paint.

Wow, that's my first thought too!

Blacklights are fairly cheap. And making one, while it would be a great experiment, would probably be more than the actual cost of a blacklight, and would be a pain in the rear.