Sylvania AN-20 Incandescent Induction RF Lamp

The RF lamp is an extremely high brightness light source, heated to incandescence by radio frequency induction. It was created in 1955 for the motion picture industries of Hollywood and New York, to increase the speed of printing projection films for circulation to cinemas around the world.

Movie film printing is a slow process, requiring the individual exposure of millions 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 The RF lamp is believed to have been superseded by the xenon short arc during the 1960s.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. 1955-1960
Original Value: Unknown
References: 1) X-Ray shadowgraph taken at 160kV 15μA.
2) Primer of Lamps and Lighting, W. Allphin, publ. Sylvania Electric Products Inc., 2nd Edition 1965, p.144.
3) IES Lighting Handbook, publ. Illuminating Engineering Society of New York, 5th Edition 1972, p.8-17.
4) US Patent 2,966,601, Induction Lamp, Sylvania, S.C. Peek, Filed 08-Jul-1955.
5) US Patent 2,774,905, Induction Lamp, Sylvania, F.N.C. Hansen, Filed 08-Jul-1955.
6) US Patent 2,776,391, Induction Lamp with improved life, Sylvania, S.C. Peek & J.F. Waymouth, filed 30-Dec-1955.
7) US Patent 2,803,774, Induction Lamp with improved uniformity, Sylvania, L.H. Sabine, filed 16-Feb-1956.
8) US Patent 2,842,698, Induction Lamp with improved uniformity, Sylvania, S.C. Peek, filed 30-Mar-1956.
9) US Patent 2,948,826, Induction Lamp with improved maintenance, Sylvania, W.H. Hay & F.N. Hansen, filed 09-Apr-1956.
10) US Patent 2,856,269, Purifying Induction Lamp Target, Sylvania, L.H. Sabine & S.L. Willey, filed 28-Feb-1956.