||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.
GEC was unique to offer the 160W model, and it is believed that it was introduced to compete with Thorn's high efficacy 140W lamp since it is also designed for 0.9 Amp operation. In order to achieve optimum efficacy it probably employs the superior indium-tin oxide film, whereas the 200W and 60W versions are believed to have used the earlier tin oxide material. Its construction is similar to the 200W lamp aside from the visible difference in film colour, and the grooves of the discharge tube being deeper so as to maintain optimum sodium vapour pressure at its lower power loading. The electrodes are of the beehive shape SOX-type.
Its efficacy is considerably less than Thorn's 140W lamp, presumably owing to the difference in discharge tube cross-section. This may explain why the GEC 160W model was not a great commercial success.