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Sylvania AN-20 Incandescent Induction RF Lamp |
Movie film printing is a slow process, requiring the individual exposure of thousands of frames for every copy. For fast and consistent printing, the light source must combine extreme high brightness with perfect stability and uniformity. Carbon arcs used in cinema projection were not sufficiently stable, and compact tungsten and zirconium arc lamps were not powerful enough. Film printers therefore relied on solid-source incandecent lamps using multiple adjacent filaments in parallel. These required diffusing optics to achieve the necessary uniformity, which meant that only ~7% of lamp output was usable and this severely limited printing speeds.
The RF lamp excels in brightness, with <4% non-uniformity. The light source is a refractory target of tantalum carbide, 5/16" diameter, supported on a zirconia tube to minimise heat loss. An externally-applied RF field is focussed onto the target by a copper cylinder, which has a slit to avoid its own heating, and is water-cooled via copper pipes sealed through the base posts of the lamp. Mica sheets prevent its contact with the glass bulb, which has an optically flat ground glass window. The bulb contains argon or krypton to minimise heat loss, filled to high pressure via a metal tubulation in one of the base posts. Life is extended by adding a trace of hydrogen, which limits blackening by forming hydrocarbons as the target decomposes. The RF lamp is believed to have been superseded by the xenon short arc during the 1960s.
| Manufacturer: | Sylvania Electric Products Inc. | |
| Lamp Power: | Determined by RF Generator | |
| Lamp Voltage: | N/A | |
| Lamp Current: | N/A | |
| Lamp Frequency: | Approx. 4 megahertz | |
| Cap Type: | G38 Mogul Bipost | Water Union fittings |
| Bulb Type: | T-63 | T-20 in eighths/inch |
| Bulb Finish: | Clear optically flat window | Borosilicate glass |
| Light Source Type: | TaC Button | 5/16" diameter |
| Atmosphere: | Argon +5% hydrogen | 1.5 bar fill pressure |
| Luminous Flux: | 5,000 lumens | in 50° solid angle |
| Luminance: | 54,000,000 cd/m² | 35,000 cd/in² |
| Colour Temperature: | CCT: 3600K | |
| Colour Rendering: | Ra 100 | |
| Chromaticity Co-ordinates: | CCx: 0.400 | CCy: 0.389 |
| Lifetime: | 75 hours | |
| Burning Position: | Universal | |
| Overall Length: | ||
| Factory: | Boston St. / Loring Av. | Salem MA, U.S.A. |
| Date of Manufacture: | Approx. 1956-1960 | |
| Original Value: | Unknown | |
