Philora 2nd Generation SO/H (SO 400)

This early low pressure sodium lamp is representative of the second generation of positive column SO/H lamp produced by Philips. The name SO 400 indicates Sodium vapour with Oxide-coated cathodes, and the number 400 refers to its approximate luminous flux in dekalumens.

The original SO lamps were made using a glass having a particularly high affinity for the argon component of the gas fill, which is required to facilitate ignition of the discharge. In order to ensure that sufficient argon remained until the lamp was in any case useless on account of its failure due to lumen depreciation, a relatively high fill pressure was required. However increased gas pressure leads to a rather low lamp efficacy, due to wastage of energy from electrons colliding with the rare gas instead of sodium vapour.

This lamp uses a superior glass developed in 1937, having a reduced tendency to adsorb argon. It permitted a reduction in the gas filling pressure without life reduction, and brought a consequent increase in luminous efficacy of about 20%. In order to keep the luminous flux of these post-1937 sodium lamps approximately the same as their predecessors, their voltage was adjusted so as to reduce power consumption. It was at this time that the standard ratings of 45W, 60W, 85W and 140W for the SO/H lamps was established.

Note the intense reddish coloration of the discharge in the gas filling, taken immediately after striking the discharge, which is due to the low fill pressure. Sodium lamps made in later years never returned to such low pressures, because as lamp lifetime was further extended, a return to higher gas fill pressures once again became necessary.
Manufacturer: Philips Gloeilampenfabrieken
Lamp Power: 60 Watts
Lamp Current: 0.6 Amps 0.54A Starting Current
Lamp Voltage: 100 Volts 450V ignition
Cap Type: By22d Porcelain
Bulb Type: Inner: TU-14 (TU-4½") Dewar: TA-50 (TA-16")
Bulb Finish: Inner: Borate Soft Glass Dewar: Clear Soft Glass
Electrodes: CC-4 Beehive BCT emitter
Arc Length:
Atmosphere: Inner: Na | NeAr Outer: Vacuum
Luminous Flux: 4,200 lm (@ 0hrs)
Luminous Efficacy: 70 lm/W (@ 0hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 2,000 hours 50% survival
Warm-up & Re-strike time: 20 minutes Instantaneous
Burning Position: Horizontal ±15°
Overall Length: 300 mm 11¾ inches
Light Centre Length: 170 mm 6¾ inches
Factory: Eindhoven Netherlands
Date of Manufacture: Inner: 1938 Wk18 (E18) Dewar: 1938 Wk15 (E15)
Original / Present Value: Unknown
References: 1) Low Pressure Sodium Lamps, J.W. Denneman, IEE Proceedings V.128 No.6, September 1981, pp.397-414.