Bamboo Style SO/H Low Pressure Sodium
In 1955 a new type of borate glass was developed by Philips, which was more resistant to the attack of sodium vapour than any type previously employed.  Low pressure sodium lamps had always been plagued by a rapid staining of the discharge tube glass, which acquired a brownish colour after a few hundred hours of operation and subsequently darkened during lamp life.  Thus although sodium lamps were supremely efficient when new, their efficacy and light output fell rapidly.

The new Philips glass offered the possibility to overcome this issue, but a number of other problems had to be solved.  One notable feature was the poor adhesion of liquid sodium to its surface.  The metal ordinarily exists as small beads, but on the new glass it spread out into large thin films.  If lamps were not burned absolutely horizontally, the sodium would also flow from one end of the lamp to the other forming large light-blocking mirrors, which offset the gain in efficacy from the improved glass.  To prevent the movement of sodium, the glass tube was rilled-in at several points leading to the so-called Bamboo construction.  This successfully overcame the sodium film problems and improved lumen maintenance.

A further problem of the glass was its exceptionally rapid absorption of the argon component in the starting gas mixture.  Argon could not be used at all and the gas filling had to be changed to a neon-xenon-helium mixture which offered similar ignition properties.  The presence of Xenon however increased the energy losses within the discharge and caused a fall in initial lumen output.  However such was the improvement in the non-staining glass that this lumen level remained much more constant, and throughout lamp life the average light output exceeded that of the former types.
Manufacturer: NV Philips Gloeilampenfabrieken
Lamp Power: 85 Watts
Lamp Current: 0.60 Amps 0.54A Starting current
Lamp Voltage: 140 Volts 200-250V Mains voltage
Cap Type: BY22d Porcelain Small
Bulb Finish: Clear Soft glass arc tube
Bulb Type: Inner: TU-14½ x 32 Outer: TA-50
Overall Length: 425 mm 16¾ inches
Light Centre Length: 230 mm 9 inches
Arc Length:
Electrodes: CCC-4 Triple Coil Black W + BCT Emitter
Atmosphere: Na | Ne-Xe-He Outer: Vacuum
Luminous Flux: 6,000 lm (@ 100 hrs)
Luminous Efficacy: 70.6 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra-44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Burning Position: Vertical Base Up ± 95°
Rated Lifetime: 6,000 hours to 50% survival
Warm-up & Re-strike Time: 12 minutes Instantaneous
Factory: Emmasingel, Eindhoven The Netherlands
Date of Manufacture: Inner: July 1960 Dewar: November 1950
Original & Present Value: Unknown