New Lamps for Old
Page 41
If you've noticed an error in this article please click here to report it so we can fix it.
Coiled-coil Filaments to Give Economy and Efficiency
ANEW range of high-efficiency lamps has been announced by the Electric Lamp Manufacturers' Association of Great Britain, Ltd., 2, Savoy Hill, London, W.C.2. They are known as the coiled-coil filament type and give a much increased light output for the same cu?rent consumption, thus ensuring greater economic value. The range includes 40, 60, 75 and 100-watt sizes in pearl, opal and clear bulbs, with an average life of 1,000 hours.
In the old squirrel-cage lamp the filament operated in vacuum, then the best-known method of preventing oxidation, but there was considerable evaporation of the filament.
In the ordinary gas-filled lamp the filament was surrounded by inert gas, originally nitrogen and later argon, which greatly restricted evaporation and even partially returned to the filament the particles of tungsten driven off. Thus the lamp could be run hotter than was possible in a vacuum type. Normally a filament would be cooled more in a gas than in a vacuum and
would, therefore, give less light. In the single-coil filament, however, the higher working temperature possible in the gas more than counterbalanced the extra cooling effect, and the light output was improved.
Coiling the coil again causes the filament to behave as an even shorter and thicker type, thereby further reducing the cooling effect. The heat so saved enables a larger filament to be used, and it is this extra surface which gives the additional light. The actual increase in light output. varies from 10 per cent, in the 100-watt type to 20 per cent. in the 40-watt.
There will be no increase in the prices of these lamps, and the characteristics of consistency, life and maintenance of light will be kept at the same high level as in the lamps which will be replaced. They are now available in all ordinary sizes in the following makes:—Bell, Cosmos, Cryselco, Ediswan, Elasta, Mazda, Osram, Philips, Siemens, Stella. Their manufacturers are, of course, all included in the membership of the Association.