Osram SOI/H Integral Sodium - Experimental

Illustrated here is an experimental sodium lamp made at Osram's Shaw lamp works. A significant shortcoming of the SOI type lamp was that because the discharge tube was enclosed by high vacuum, the electrodes end of the discharge tube would run hotter than the U-bend end. This resulted in sodium being distilled from hot areas to cold over life, thus hotter regions of the discharge tube became depleted of sodium and luminous efficacy fell.

Philips attacked this problem by blowing small dimples into the sides of the discharge tube, which naturally ran at a cooler temperature. Sodium would condense in the dimples and remain there during lamp life, ensuring a superior sodium vapour uniformity and better lumen maintenance.

However, dimples could not be used with the GEC's design in which a close-fitting glass insulation sleeve was slipped over each limb of the discharge tube. Philips lamps sacrificed efficacy by employing one large sleeve over the whole discharge tube, large enough to accommodate the dimples. To create a similar cooling effect without loss of efficacy, this sample was tested in which the sleeves have holes in the side through which some heat is able to escape. There was a small drop in initial efficacy due to heat loss through the holes, however the idea was that average efficacy through life would improve. It is, however, evident from the sodium position in this sample that the technique was not successful - presumably the cooling effect was not great enough to encourage sodium condensation. Consequently this test lamp was not marketed, and GEC's SOI lamps were prone to sodium migration until the problem was solved with later SOX lamps having graded insulation along the length.
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