Osram-GEC First Coiled-Coil Tungsten GLS

Although the idea of a coiled-coil filament dates back to a 1914 patent, it took many years before tungsten metallurgy had been refined to the extent that such a lamp could be made. In 1927 a coiled-coil projection lamp with compact filament was introduced by GE of USA, but it was plagued by filament sag and short life. An experimental 230V 40W GLS lamp was briefly introduced in Britain in 1933, but also withdrawn due to similar shortcomings. The problem was finally solved in 1934 when a new filament stabilisation technique was developed by Osram in Europe, leading to the launch of this lamp. The Americans followed suit in 1936.

The coiled-coil is advantageous because heat losses to the gas filling are proportional to filament length, but hardly influenced by coil diameter. The extra coiling leads to a filament of shorter aspect ratio, thereby elevating luminous efficacy. The gain is greatest for low wattage filaments which tend to have higher length-to-diameter ratios, being about 20%, 15%, 10% and 7½% for 40W, 60W, 100W and 150W ratings respectively. Below 25W there is no benefit since such types are vacuum and have no gas filling.

This early lamp employs 3 filament supports, and was produced almost without change until 1956 when one was eliminated to realise a small cost reduction. It is interesting to note that the stem tube contains no fuse wire, that feature not being added until the later 1930s when it was discovered that CC lamps were much more prone to flashover at end of life. The gas in this lamp displays an interesting greenish colour with long afterglow when ionised, presumably due to cyanogen radiation which is indicative of an unusually low moisture and oxygen content in the gas.
Manufacturer: The General Electric Company of England
Lamp Power: 60 Watts
Lamp Voltage: 240 Volts
Lamp Current: 0.25 Amperes
Cap Type: B22d/25x26 Brass+Vitrite
Bulb Type: PS-65 PS-20½ in eighths/inch
Bulb Finish: Clear Soda-lime silicate glass
Filament Type: CC-9 3x supports
Atmosphere: 85:15 Ar:N2 approx. 0.9 bar
Luminous Flux: 690 lm @ 1 hour
Luminous Efficacy: 11.5 lm/W @ 1 hour
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2700K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.460 CCy: 0.411
Rated Lifetime: 1000 hours to 50% survival
Burning Position: Universal
Overall Length: 117.5±3.5 mm 43/4 inches
Light Centre Length: 85±3 mm 31/8 inches
Factory: Wembley United Kingdom
Date of Manufacture: November 1934 Date Code: 2 11
Original Value: GB £0 1s 9d (1937)
References: 1) Osram-GEC Lamp Catalogue, 1937 UK, pp.5,11,13
2) Osram-GEC Brochure, 1934 UK
3) The Development of Tungsten Filament Lamps, Ray Burgin (Osram-GEC), Lighting Research & Technology V.16 No.2 1984 pp.61-72
4) BTH Reminiscences - Sixty Years of Progress, H.A. Price-Hughes (BTH Rugby), publ. BTH 1946 UK, p.71
5) Lengthening The Day, B. Bowers (The Science Museum, London), publ. Oxford University Press 1998 UK, p.153
6) The Electric Lamp Industry, A.A. Bright, publ. The Macmillan Company 1949 USA, p.328-329
7) GB Patent 6439, 13th March 1914