GE-Mazda Silver Bowl Indirect Light
Silver Bowl incandescent lamps were invented in 1933 by the Silvray company of New York, and quickly set a new trend in glare-free indirect lighting of indoor spaces. Silvray was not a lampmaker, but established the first durable and cost-effective process of applying mirror coatings to lamps. These were applied to the neck, bowl, or side of ordinary pear-shaped lamps. The company marketed a successful line of fixtures based on the silver bowl lamps, in which they were suspended base-up to floodlight the ceiling. Owing to the complete obscuration of the filament from view, a room could be indirectly lit with very low glare. They were used in white enamel reflector fixtures in high powers up to 1000W.

The coating consists of a chemically-desposited mirror of highly reflective pure silver applied to the outer surface of the glass. To prevent degradation it is then sealed under an electroplated layer of copper. The resulting coating is very fragile, and scratch resistance is improved with a top coat of durable aluminium flakes applied by a painting process. The luminous flux is approx. 7% lower than uncoated lamps.

Although the main lampmakers soon offered silver bowl lamps, these were all coated by Silvray owing to that company's strong patent situation and refusal to license its process. This particular lamp is one of the first engineering samples tested by General Electric in the mid 1930s. These early silver bowl lamps were very expensive, costing around three times the price of uncoated lamps. They were superseded by a lower cost version based on an internal aluminium coating soon after GE had developed the vacuum metallizing process in 1936, in which an aluminium mirror is evporated onto the glass under high vacuum.
Manufacturer: General Electric U.S.A.
Lamp Power: 100 Watts
Lamp Voltage: 120 Volts
Lamp Current: 0.83 Amperes
Cap Type: E26s Brass + vitrite
Bulb Type: A-75 A-23 in eighths/inch
Bulb Finish: Silver Bowl Frosted Soda-lime glass
Filament Type: CC-6/1s Transverse Coiled-Coil
Atmosphere: Argon-Nitrogen
Luminous Flux: 1420 lumens
Luminous Efficacy: 14.2 lm/W
Luminous Intensity: N/A
Beam Distribution: 100% Upward
Colour Temperature & CRI: CCT: 2950K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.440 CCy: 0.407
Rated Lifetime: 750 hours
Burning Position: Universal
Overall Length: 154 mm 61/16 inches
Light Centre Length: 111 mm 43/8 inches
Factory: Youngstown, Ohio U.S.A.
Date of Manufacture: Approx. 1935 Date Code: . .
Original Value: US $0.70 (1936)
 
References: 1) Illumination by Silvray, 1933 USA
2) GE Large Lamp Catalog, 1936 USA
3) GE Large Lamp Catalog, 1937 USA
4) Mazda Lamps Characteristics & Applications, C.E.Weitz, General Electric U.S.A., August 1939 p.32.
5) General Electric Lamp Bulletin, C.E.Weitz, General Electric U.S.A., May 1946, p.30.
6) Industrial Electric Lamps and Lighting, E.S.Lincoln, publ. Essential Books, 1945, p.21, pp.200-201.
7) Lamps for a Brighter America, P.W.Keating, publ. McGraw-Hill Book Company Inc., 1954, pp.160-161.
8) A Century of Light, J.A.Cox, publ. The Benjamin Company Inc., 1979, p.89.
9) Photoelectric measurement.