Monster Ride Op, the brightest electric lights you can get are arc lights...where the light is produced by a high-voltage spark jumping across a small gap. Too bright for most general lighting, but great for projection. So the technology was adapted for theatrical projectors. Inside the projector is either a pair of carbon rods or a carbon rod and a metal plate. The rods are adjusted to almost touch each other, and a high voltage current is passed through the rod to generate the spark. Unfortunately, as it arcs, the end of the carbon rod burns away, increasing the size of the gap which will eventually cause the spark to quit, so an advancing mechanism has to keep feeding more rod into the projector. If I remember correctly, the projectors at the Ohio Theater use a rod that is about 3/8" in diameter and about 8" long; the projectionist I was talking with said it would last through about two reels; just then it broke in mid-reel.
Modern theatrical projectors use a lamp which has two itty bitty carbon or metal rods sealed into a quartz bulb filled with xenon gas. The principle is exactly the same, except that by keeping air away from the rods, the rods don't burn, so the lamp works, maintenance free, until it doesn't anymore. Actually I have such a lamp...burned out, from a data projector, on my desk here someplace...
--Dave Althoff, Jr.
Who apologizes for straying so far off-topic...