||Less than five years after Osram-GEC introduced its Golden Linear 60W and 175W lamps having an IR film of gold, the coating was replaced by a semiconductor film of tin oxide. The new material had been pioneered with the 1964 advent of the Philips SOX range, a technology that its competitor was swift to copy for the GEC SOX lamps. In 1967-68 the film was improved again with the superior indium-tin SOX.
It is not known precisely when GEC first applied these coatings to linear sodium, however private communication with former staff estimates the date at around 1964-66. Certainly by 1969 the company's literature confirms its use in all three ratings of 60W, 160W and 200W. Thorn had also launched its semiconductor-coated SLI 140W in 1966 - which may have pre-dated the GEC's use of this material.
This 200W model is believed to have superseded the earlier 175W Golden Linear, and was marketed as an equivalent to the Thorn 200W. The new film allowed a considerable reduction in manufacturing cost and complexity. However its performance claims are surprisingly low. The initial luminous flux is only 20,500lm - just 2.5% greater than its 175W predecessor but for 14% increased power consumption, so considerably less efficient. The GEC 200W linear sodium falls even further short of the claim of Thorn's 200W lamp, which claimed 25,000lm - perhaps because GEC maintained the original crescent-shaped discharge tube for its linear sodium range whereas Thorn changed in 1966 to a superior clover-leaf section having a greater surface area to volume ratio. Despite the surprisingly low efficacy the GEC lamps were equally popular - possibly having been sold at lower prices to secure their continued place in the market.