|Huge light bulb.
This bulb looks like a grotesquely overgrown projector bulb or headlamp. The envelope of glass, while as big as an ordinary household bulb, is small compared to the size of the filament, which makes me think it's almost certainly fused quartz designed to operate at very high temperatures.
When a tungsten filament is glowing white-hot, a small amount of tungsten slowly boils off the surface of the filament and condenses on the inside of the glass envelope of the bulb. This causes two problems, first the filament eventually gets too thin and fails, and second the bulb slowly darkens due to the tungsten film being deposited on the glass.
Bulbs like this reduce this problem by putting the glass very close to the filament, and using gases with relatively high thermal conductivity inside, resulting in a very, very hot glass surface that tends to re-evaporate any tungsten that lands on it. Thus the bulb doesn't darken, and some of the tungsten that evaporates off the filament ends up condensing back on it.
This re-condensation means that, at a given operating temperature, the filament will last longer. Alternately, it means you can get the same life while operating the filament at a higher temperature. The higher the temperature the more efficient the bulb, and the whiter the light.
At 2000W this is a big bulb, but I'm not sure what it was used for, or whether it's still in common use. Many high-power applications like projectors and search lights now use xenon arc lights, which are much more efficient.
Source: Nick Brandenburg
Contributor: Nick Brandenburg
Acquired: 10 February, 2007
Text Updated: 29 January, 2009