GEC SuperSOX Miniature 18W

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.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 18 Watts
Lamp Current: 0.35 Amps
Lamp Voltage: 55 Volts 280V Ignition
Cap Type: BY22d Mycalex Insulator
Bulb Type: T-50 T-16 in eighths/inch
Bulb Finish: Indium-tin oxide film Soda-lime glass
Electrodes: CCC-4 Beehive Black W + BCT emitter
Arc Length:
Atmosphere: Na | 98.5% Ne, 1.5% Ar Outer: Hard Vacuum
Luminous Flux: 1,800 lm (@ 100 hrs) 1,600 lm (@ 2000 hrs)
Luminous Efficacy: 100 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 10,000 hours 70% survival
Warm-up & Re-strike time: 8-12 minutes Instantaneous
Burning Position: Vertical Cap Up ± 110°
Overall Length: 210 mm 8sup>1/4 inches
Light Centre Length: 130 mm 51/8 inches
Factory: Shaw, Oldham England
Date of Manufacture: August 1981 Date Code: NH
Original / Present Value: GB £15.13 (1988) GB £36.23 (2014)
References: 1) Osram-GEC Lamp Catalogue, UK, 1985/86, p.219
2) Osram-GEC Low Pressure Sodium Lamps Brochure, 1981.
3) Osram-GEC UK Price List, December 1988.