Philips SOI Integral Sodium Vapour - 2ndGeneration
Following on from the gains in luminous efficacy attained by adopting the integral lamp design which reduced conducted and convected thermal losses, Philips next focussed their attention on reducing the loss of radiated heat from sodium discharge tubes.

It was well known that the glass outer jacket of the lamp was opaque to certain wavelengths of infrared radiation (heat) and that in itself, it would send about 50% of the radiated heat back to the discharge tube.  Aiming to increase this figure, Philips enclosed the discharge tube within a second glass sleeve and sealed this whole assembly into the integral outer bulb.  The effect is that each additional sleeve of glass redirects about 50% of the heat back to the discharge tube but absorbs about 3% light output.  A good compromise was found using one additional sleeve, as in this lamp - a second sleeve would have slightly increased efficacy, but resulted in heavy and fragile lamp designs.  Adding a third sleeve would have actually reduced efficacy due to extra light absorption.

For many years this design was the standard sodium lamp design offered by Philips.  Meanwhile, Osram-GEC of England offered higher efficacy lamps with one sleeve over each limb of the discharge tube, however it was not possible to use sodium-retaining dimples in this design so the GEC lamps were more prone to the deleterious effects of sodium migration.

This Philips lamp has been perfectly assembled down to every detail, almost as a work of art.  The thumbnail photos show in detail how the additional glass sleeve is mounted.
Manufacturer: NV Philips Gloeilampenfabrieken
Lamp Power: 140 Watts
Lamp Current: 0.90 Amps 0.81A Starting current
Lamp Voltage: 160 Volts 200-250V Mains voltage
Cap Type: BY22d Porcelain Insulator
Bulb Finish: Clear Soft glass arc tube
Bulb Type: Inner: TU-17 x 40 Outer: T-65
Overall Length: 525 mm 20¾ inches
Light Centre Length: 290 mm 11½ inches
Arc Length:
Electrodes: CCC-4 Black Tungsten BCT emitter
Atmosphere: Na | 99% Ne, 1% Ar Outer: Hard Vacuum
Luminous Flux: 13,000 lm (@ 100 hrs) 12,200lm (mean to 4000hrs)
Luminous Efficacy: 92.9 lm/W (@ 100 hrs) 87.1lm/W (mean to 4000hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra-44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Burning Position: Horizontal ± 5°
Rated Lifetime: 6,000 hours
Warm-up & Re-strike Time: 11 minutes Instantaneous
Factory: Emmasingel, Eindhoven The Netherlands
Date of Manufacture: February 1962
Original & Present Value: £4 9s 0d (1960) £68.59 (2005)
 
References: 1) Philips UK Lamp Catalogue, 1960.