Solarcolour Plug-In SON-I 310W

Osram-GEC was the first company to bring HPS technology to Europe, with 15 lamps being set up along a 1450-foot stretch of road outside the factory on East Lane, Wembley in January 1966. They were based on GE's original 400W lamp.

Within two years GEC made a significant design departure from its competitors. A drawback of the original lamps was the difficulty upgrading existing mercury installations. Firstly, the failure of HPS lamps is caused by rising arc voltage over time, so to attain a reasonable life it must start with a lower voltage. To keep power ratings the same as mercury lamps, this requires higher current and new ballasts. Secondly, the control gear is made more complex by the requirement for a high voltage pulse to strike the arc. GEC recognised that if it could make its lamps work on existing mercury control gear it would have a greater market potential, and by doing just that it quickly grew to a dominant force in the HPS business.

GEC developed its lamps with a low arc voltage for long life, but accepted a compromise by allowing lamp power to drop to non-standard ratings when used on existing mercury ballasts. This 310W model was the first of the company's "Plug-In" series, designed for operation on 400W mercury ballasts tapped to 10V above the actual supply voltage. The ignition problem was solved with the development of the internal snap-starter - a bi-metal switch heated by a loop of nichrome wire, arranged in parallel with the arc, which creates an inductive pulse to strike the discharge.

Also of interest in this lamp are the early disc-type niobium seals of the arc tube. One end is blind, while the other contains sodium amalgam in the crimped-off exhaust tube.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 310 Watts
Lamp Current: 3.2 Amps 4.4A during starting
Lamp Voltage: 110 +20-15 Volts 1000V ignition
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Type: TD-51 TD-16 in eighths/inch
Bulb Finish: Clear Borosilicate glass
Electrodes: Backwound Tungsten BCT Emitter
Arc Length: 90 mm 31/2 inches
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 27,000 lm (@ 100 hrs) 25,000 lm (average)
Luminous Efficacy: 87.1 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 23
Chromaticity Co-ordinates: CCx: 0.526 CCy: 0.418
Rated Lifetime: 6,000 hours 80% survival, 90% lumens
Warm-up & Re-strike Time: 5 minutes 15 minutes
Burning Position: Universal
Overall Length: 292 mm 111/2 inches
Light Centre Length: 175 mm 67/8 inches
Factory: Shaw, Oldham England
Date of Manufacture: October 1969 Date Code AK10
Original / Present Value: AU $41.77 (1972) GB £185 (2013)
References: 1) Osram-GEC Lamp Catalogue, Australia, 1969, p.45
2) Osram-GEC Technical Data, High Pressure Sodium Lamps L1/4 HT/EX, 1976
3) Osram-GEC Solarcolour Brochure, 1972
4) Osram-GEC Solarcolour Brochure, 1981
5) Osram-GEC Solarcolour Brochure, c.1985
6) Osram-GEC Solarcolour Plug-In Brochure, 1972
7) Osram-GEC Price List, Australia, February 1972