GEC SuperSOX 90W - 4th Generation

Osram-GEC's Low Pressure Sodium SOX lamps underwent a number of design changes over the years, and this lamp is representative of the company's 4th generation design.

The first generation lamps from 1964 employed a heat-reflective coating of tin oxide and had dimpled discharge tubes. These were superseded in 1967 by the 2nd generation design in which the IR coating was changed to the superior indium-tin oxide. Before 1969 the 3rd generation lamps had been introduced, in which the dimples were eliminated and replaced by ring-shaped sodium reservoirs around the U-bend. In parallel a new top support was introduced to yield a mechanically more robust design, in which the U-bend was held on an electrically insulated tube of steatite ceramic, and a large mica disc was provided to offer some thermal insulation and reduce heat losses in the area of the U-bend.

This lamp is representative of the 4th generation design, which is believed to have been introduced soon after Philips' development of the 18W SOX lamp in 1977, in which the importance of further improving heat insulation at the U-bend became apparent. The major design change in this 4th generation lamp is the introduction of a nickel plated steel disc at the dome end of the lamp. The mica disc of the earlier lamps is still retained but its diameter is reduced since it no longer performs any thermal role. It serves only as a mechanical cushion to prevent scratching of the delicate tip-off area by the metal disc. In parallel, the metal fingers of the top support which engage with the outer bulb have been extended in length so as to prevent accidental tilting of the metal disc, keeping it perpendicular to the plane of the discharge tube for optimal heat reflection.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 90 Watts
Lamp Current: 0.95 Amps
Lamp Voltage: 112 Volts 420V Ignition
Cap Type: BY22d Phenolic Insulator
Bulb Type: T-65 T-20½ in eighths/inch
Bulb Finish: Indium-tin oxide film Soda-lime glass
Electrodes: CCC-4 Beehive Black W + BCT emitter
Arc Length:
Atmosphere: Na | 99% Ne, 1% Ar Outer: Hard Vacuum
Luminous Flux: 12,750 lm (@ 100 hrs) 12,500 lm (average to 4,000h)
Luminous Efficacy: 141.7 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: >6,000 hours 50% survival
Warm-up & Re-strike time: 15 minutes Instantaneous
Burning Position: Vertical Cap Up ± 110°
Overall Length: 518 ± 10 mm 20½ inches
Light Centre Length: 285 mm 11¼ inches
Factory: Shaw, Oldham England
Date of Manufacture: February 1983 Date Code: QB
Original / Present Value: GB £20.58 (1988) GB £49.28 (2014)
References: 1) Osram-GEC Lamp Catalogue, UK, 1985/86, p.219
2) Osram-GEC Technical Data, Low Pressure Sodium Lamps L4/HT, October 1969
3) Osram-GEC Low Pressure Sodium Lamps Brochure, 1972
4) Osram-GEC Low Pressure Sodium Lamps Brochure, 1981