Osram SOI/H Integral Sodium - Experimental

One of the drawbacks of the GEC SOI/H lamps was the tendency for sodium to migrate along the discharge tube during life, leaving some parts of the lamp devoid of sodium and with reduced light output. This was due to the natural effect that the heat generation near the electrodes caused that end to operate at high temperature, while the reduced thermal insulation at the U-bend caused that to run cooler. In the evacuated outer bulb of the Integral lamps, there is no gas convection effect to homogenise the temperatures.

To a certain extent this also affected the dewar type lamps, and was partly overcome by Philips' 1958 invention of the Sodium Dimples. These naturally ran cooler and slowed the rate of sodium distillation, leading to better lumen maintenance and life. However, dimples could not be used with GEC SOI lamps in which a close-fitting glass insulation sleeve was placed over each limb of the discharge tube.

In this experimental lamp, small holes have been melted in the sleeves through which heat can escape. It is evident from the sodium position that the technique was not successful - presumably the cooling effect was not great enough to encourage sodium condensation. Consequently this design was not marketed, and GEC's SOI lamps were prone to sodium migration until the problem was solved with the SOX lamps having graded insulation along the length. Incidentally, Philips later introduced dimpled SOI/H lamps, achieved by employing a glass heat-reflection sleeve large enough to accommodate the entire dimpled discharge tube. However the reduced thermal insulation vs the GEC lamps required narrower bore discharge tubes, operating at higher current density and consequently with lower lamp efficacy.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 140 Watts
Lamp Current: 0.9 Amps 0.81A Starting Current
Lamp Voltage: 160 Volts 450V ignition
Cap Type: By22d Mycalex & Brass
Bulb Type: T-65 T-20½ in eighths/inch
Bulb Finish: Clear Soda-lime glass
Electrodes: CCC-4 Beehive Black W + BCT emitter
Arc Length: 600mm
Atmosphere: Inner: Na | Ne Ar1% Outer: Hard Vacuum
Luminous Flux: 9,800 lm (average)
Luminous Efficacy: 70 lm/W (average)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 6,000 hours 70% survival
Warm-up & Re-strike time: Approx. 15 minutes Instantaneous
Burning Position: Horizontal ± 20°
Overall Length: 518 ± 10 mm 20¾ inches
Light Centre Length: 280 ± 10 mm 11 inches
Factory: Shaw, Oldham England
Date of Manufacture: July 1958 Date Code PG
Original / Present Value: N/A (Engineering Sample)
References: 1) Osram-GEC Lamp Catalogue, UK, 1959-60, p.19
2) Private Communication, Alan Prest & Peter Anderson, Osram Lamp Works, Shaw, UK, 2000
3) A New Sodium Lamp, E.H. Nelson & S.A.R. Rigden, Light & Lighting August 1956 pp.217-220
4) UK Patent 801,482, Improvements in or Relating to Sodium Vapour Electric Discharge Lamps, S.A.R. Rigden, Filed Jan. 27th 1955
5) UK Patent 826,751, Improvements in or Relating to Sodium Vapour Electric Discharge Lamps, E.R. Dinan & S.A.R. Rigden, April 30th 1956