||Further to Philips' launch of the Mini-SOX 18W lamp in 1977, its competitors attempted to solve the same technical barriers to its development in their own ways. Osram-GEC had achieved success by 1981, and Thorn Lighting did not offer an 18W lamp until 1988.
The Philips 18W lamp required a new construction to deliver good performance at such low power. A close-fitting heat reflector was added to the periphery of the U-bend to minimise thermal gradients along the discharge tube, which would otherwise result in short life and low efficacy.
With the Osram-GEC design this feature is not present - the U-bend is insulated only by the same nickel plated steel flat disc as used on the larger SuperSOX lamps. Possibly this is owing to this company's application of a graded thickness IR coating to the outer bulb, which naturally ensures a more uniform temperature gradient along the discharge tube than in Philips lamps which have a constant IR coating thickness.
The GEC 18W lamp is filled with 1.5% argon in neon, higher than the 1% that is usually employed. This is needed to achieve a sufficiently long lamp life, but has the drawback of raising ignition voltage. That problem has been attacked with two small metal springs, which connect one of the lamp terminals to the electrically conductive IR coating, which itself serves as an auxiliary ignition electrode. Since the metal top support clip is in physical contact with the film and therefore also electrified, good electrical insulation of the discharge tube is required to avoid drawing sodium ions through the glass, and this has been achieved by reverting to the old 'bobbin' style ceramic insulators at the bend.