Philips SOI Integral Sodium Vapour - 1stGeneration

Conceived in 1955, this was the first mass produced sodium vapour lamp which dispensed with the requirement for a separate dewar vacuum jacket, previously employed for thermal insulation purposes to maximise lamp efficacy.

The dewar jacket was not a particularly efficient thermal insulator since a layer of conductive air always surrounded the discharge tubes in SO type lamps. In addition, when a hot SO lamp was switched off after a cold night's streetlighting service the air in the dewar would contract, drawing in dusty air from outside and deleterious films of condensation were also commonplace.

Sealing the discharge tube into a one-piece outer jacket both enhanced thermal insulation, raising lamp efficacy from 65 to 87lm/W, and maintained the cleanliness of the lamp for much longer. However, the turbulent air flow inside dewar jackets did ensure that the temperature of the discharge tube was fairly uniform along its length. In a vacuum environment this was no longer the case, and the electrode ends naturally operated at higher temperature. The effect was that sodium would be distilled to the bend end, depleting other regions of this light-generating metal with a consequent loss of efficacy.

To encourage sodium to remain all along the discharge tube Philips pioneered the use of dimples in the sides of the glass. Being further from the discharge, the glass here is a few degrees cooler than the rest and sodium distribution all along the tube can effectively be maintained during lamp life. This lamp exhibits the first use of these dimples, and is also superbly manufactured to a very high level of precision.
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: B22d/30x35 Ni plated brass + Vitrite
Bulb Finish: Clear Soft glass arc tube
Bulb Type: Inner: TU-12 x 28 Outer: T-38
Overall Length:
Light Centre Length:
Arc Length:
Electrodes: CCC-4 Black Tungsten BCT emitter
Atmosphere: Na | 99% Ne, 1% Ar Outer: Hard Vacuum
Luminous Flux:
Luminous Efficacy:
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:
Warm-up & Re-strike Time: 7 minutes Instantaneous
Factory: Emmasingel, Eindhoven The Netherlands
Date of Manufacture: October 1958
Original & Present Value: Unknown