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"Make your own light with Carbon goodness!

The idea behind a carbon arc light / lamp is that electricity "likes" to jump from one piece of carbon to another, creating an arc of electricity in mid-air. The tips of the carbon rods start to heat up more and more, and eventually to the point where they produce A LOT of light.

For a while, carbon arc lamps competed with your everyday light bulb, but the light bulb won out, and now probably provides most of the light in your home. A lot of people didn't like the harsh white light of the arc lamps, and sometimes the lamps would make a sound around 10,000 Hz that was really annoying. Of course, our good friend Tesla saved the day on that.

For a long time, nobody could match the sheer power of arc lamps, (at the time, they were about 200 times more powerful than filament bulbs), and so they were used in spotlights and movie theaters.

And now, you can have your own carbon arc lamp!"

Full article:
http://www.instructables.com/id/Carbon-Arc-Lights/
http://www.mig-welding.co.uk/arc-tutorial.htm
http://www.scienceclarified.com/Di-El/Electric-Arc.html

Carbon arc lamps are now more of an historical curio than an everyday source of light.
They need a lot of attention and are less efficient than modern high power discharge lamps.
Arc lamps "went out with the war" for general lighting such as street or railway station lighting, being displaced by high wattage filament lamps, once these became affordable. The higher energy use of the filament lamps was justified by them burning for 1000 hours without attention.
For specialist purposes needing a very high power point source of light, such as cinema projection, searchlights, and film lighting, arc lamps continued to be widely used into the 1970s, and no doubt a few are still in use.
Although arcs can use AC or DC, the later is preferred for the brightest and most stable arc.

If considering experimenting with any form of home made arc lamp, please take great care.
Dangerous voltages are involved, the light is dangerous to the eyes and skin, and fires can be started by hot particles emitted from the arc.

The one thing I very occasionally use carbons for these days is as a twin carbon arc torch. You can do basic brazing with them without the need for gas. They can also be used as a rough cutting tool. Finally, you can also use them to do welding on thin sheet steel where a stick welder would punch a hole through. In other words, where you'd ordinarily need a tig, mig or gas. You need covering up well, though, cos the UV is fierce.

Having said all of the above, a twin carbon arc torch is a bit agricultural in terms of finesse. but, it's handy if you are not too bothered about it being pretty cos it means you have everything you might need in the one stick welder with a twin carbon arc torch attachment. You just whack the volts right down and the amps right up when you use it.

Funnily enough, when it comes to using carbons for a twin carbon arc welding torch, AC is best cos it means both carbons wear down evenly and so you are not constantly having to adjust one of them.

I've included a link to one of them, below.

http://www.youtube.com/watch?v=DYnsCXVsJsw