SON-I Solarcolour High Pressure Sodium

Even in the early 1970's High Pressure Sodium lamps were still not available in ratings below 250W, but it was evident that there was a great demand for a low wattage, high efficiency compact light source. Late in 1974, Osram-GEC was first in Europe to market a small SON lamp, with its initial offering being this 120W Solarcolour model.

Having the same dimensions as a 125W MBF mercury lamp, it was ideally suited to introduce SON technology to Group B street lighting, as well as any areas where low luminaire heights ruled out the use of higher wattage SON lamps. A diffuse elliptical lamp was made to work with the optics of existing mercury lanterns, as well as this clear format for new luminaires which achieved better optical control. All lamps incorporated an internal ignitor so that no extra gear space was required in the standard mercury lanterns.

The ignitor takes the form of the GEC's classic snap-switch design. A tempered bi-metal strip with silver contacts passes a current to a nearby heater coil, all mounted on a small ceramic block. At switch-on the heater becomes incandescent and draws full current from the ballast, around which a magnetic field develops. After a minute or so, the bi-metal strip flexes and instantly breaks the whole circuit. The collapsing field around the ballast windings induces a high voltage which is usually successful in striking the arc at the first attempt. The hot restrike time is rather long though, with 15-20 minutes being required for the bi-metal to cool.

Also of interest in this lamp are the early disc-type niobium seals at either end of the arc tube. One end is blind, while the other contains sodium amalgam within the exhaust tube.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 120 Watts
Lamp Current: 1.4 Amps
Lamp Voltage: 100 Volts
Cap Type: E27s/27 Ni plated brass + vitrite
Bulb Finish: Clear Soft glass
Bulb Type: ED-75 ED-23½ in eighths/inch
Overall Length: 178 mm 7 inches
Light Centre Length: 112 mm 4½ inches
Arc Length:
Electrodes: Backwound Tungsten Barium Calcium Tungstate
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 8,600 lm (@ 100 hrs) 8,000 lm (@ 2,000hrs)
Luminous Efficacy: 71.7 lm/W (@ 100 hrs) 66.6 lm/W (@ 2,000hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 23
Chromaticity Co-ordinates: CCx: 0.526 CCy: 0.418
Burning Position: Universal
Rated Lifetime: 10,000 hours 80% survival, 90% lumens
Warm-up & Re-strike Time: 5 minutes 15 minutes
Factory: Shaw, Oldham England
Date of Manufacture: May 1976
Original & Present Value: £28.89 (1988) £51.89 (2005)
References: 1) Osram-GEC Lamp Catalogue, Australia, 1975, p.32
2) Osram-GEC Information Sheet, 120W Solarcolour, October 1974
3) Osram-GEC Solarcolour Brochure, 1981