A lamphouse is the light source for a projector. It may be a separate component or it may be built into a console or otherwise joined to the projector mechanism. Modern lamphouses designed for theatrical presentation use xenon short-arc lamps for 16mm, 35mm, and 70mm projection. Some legacy installations still employ carbon arc lampouses. Portable projectors and small gauge projectors intended for home use generally employ incandescent, halogen, or tungsten lamps.
The earliest lamphouses only contained a light source and a condenser lens to focus the light on the aperture. As the technology evolved, reflectors were added to the back of the lamphouse. Condenser lenses fell out of use after the 1930s as reflectors became more efficient.
Lamphouses that are powerful enough for theatrical presentation generate a significant amount of heat. This must be mitigated through internal blowers, external exhaust fans, dichroic mirrors, and/or heat shields. In addition to cooling, carbon arc lamphouses require exhaust to vent ozone and ash. With a two-projector changeover system, this requires a damper assembly that permits adequate ventilation without compromising the arc.
In the initial light path alignment, the lamphouse is aligned with the projector mechanism. The reflector is then aligned within the lamphouse. These adjustments are made during installation and can usually remain untouched. For xenon arc lamps the lamp is then aligned within the reflector. For carbon arc lamphouses, upon initial installation the focal length of the reflector should be determined and the carbons should be aligned so that the tip of the negative carbon is at the focal point of the reflector, and the arc gap is set for optimal light output. The shadow of the carbons is then reflected onto a paper card on the side of the lamphouse, and the projectionist marks the card to show the optimal position of the carbons. This card is used as a reference point for aligning the carbons.
Items to Add
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- lamp alignment (how-to, importance of)