White Silica 'Q-Coat' A-Line Incandescent

Almost 25 years after GE's invention of the inside frosted lamp, the next major development in light diffusion was achieved by the same engineer - Marvin Pipkin. His idea was further developed for production by D. E. Elmendorf.

Although the inside frosted lamp reduced the luminance of clear lamps about 100-fold, it still showed a pronounced hot spot. Hence it only partially displaced the earlier white glass and white sprayed lamps, which provided superior diffusion although with the penalty of about 10-15% light absorption

Pipkin's second invention was the so-called 'smoke process', in which a thin layer of extremely fine silica particles is deposited on the inner suface of an already inside frosted bulb, to further increase diffusion. The total reduction in light output depends on the coating thickness, and in practice a level was chosen that resulted in about 2% decrease, which does not eliminate the hot-spot but reduces it very considerably.

The new coating was introduced in 1949 under the Q-Coat brand, first applied on a 150W R40 mushroom shaped lamp with variable thickness coating, intended for table lamps to shine more light downwards. It was then extended to this 100W A21 lamp, next a 60W A19, and also to 3-way types, sold under the Deluxe White name. By the 1970s a full range of A-line types existed and they were known by their present name of Soft White. This particular lamp is one of the first samples, sent from NELA Park to GE's UK subsidiary BTH-Mazda for their introduction of the same process. It is unusually marked on the bulb crown by selectively removing the coating to display the rating and brand name.
Manufacturer: General Electric USA
Lamp Power: 100 Watts
Lamp Voltage: 120 Volts
Lamp Current: 0.83 Amperes
Cap Type: E26s/25 Brass & vitrite
Bulb Type: A-67 A-21 in eighths/inch
Bulb Finish: Silica Powder Soda-lime glass
Filament Type: CC-6/1s Coiled-Coil Transverse
Atmosphere: Argon-Nitrogen Red phosphorus getter
Luminous Flux: 1630 Lumens
Luminous Efficacy: 16.3 Lumens per Watt
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2700 Kelvin CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.460 CCy: 0.411
Rated Lifetime: 750 hours
Burning Position: Universal
Overall Length: 135 mm 55/16 inches
Light Centre Length: 98 mm 37/8 inches
Factory: NELA Park, Cleveland OH U.S.A.
Date of Manufacture: Approx. 1950
Original Value: US $0.15 (1937)
References: 1) Lamps for a Brighter America, Paul W. Keating, publ. McGraw-Hill, 1954, pp.226-227.
2) A Century of Light, James A. Cox, publ. The Benjamin Company, 1979, p.71.