||The incandescent lamp is an article which has endured more than a century of the fiercest imaginable competition, during which its design and manufacture has been highly refined to arrive at the lowest cost without compromising performance. One area that was attacked was the number of molybdenum wires required to support the filament. When the British 100W coiled-coil GLS lamps were launched in 1934 they had three supports. This was reduced in 1956 to two, and by the 1970s tungsten metallurgy yielded sufficient improvements that it seemed feasible to switch to a single support.
Since 1979 marked the centenary of Swan's invention of the first incandescent lamp, that seemed and appropriate date for the launch of the new lamps. Several hundred prototypes were made as promotional items, and distributed among GEC management and senior figures in the British lighting industry. Unfortunately the batch of tungsten wire in these lamps (which was produced by Lamp Metals Ltd, the GEC-Thorn tungsten factory at Gateshead) showed a slightly different crystalline structure than standard production. This was not the intention and with two support wires this small variation would have gone un-noticed and had no consequence, but with one support it led to too much filament sag, and a small reduction in lamp lifetime.
As a consequence of the Centenary Lamp run, it became clear that before the GEC could implement the switch to a single support wire, it would have to invest in better process controls both at the tungsten wire factory in Team Valley and during lamp production. Such investment would have outweighed the small saving in material cost by eliminating one support wire, hence the change was never made.