Philora Direct Current Sodium Vapour

This sodium lamp bears many similarities in its construction to the Philips' original 4000-lumen DC lamp, but is considerably smaller in dimensions. A clear record of its existence has not been found in any literature which makes it particularly difficult to identify. It is believed to have been constructed as a small source of monochromatic sodium radiation for laboratory use. Its size is comparable to GE's NA-1 Sodium Lab-Arc which was constructed for a similar application, and this lamp is presumed to be of similar power, i.e. approx. 500 lumens. It seems probable that Philips manufactured it for the same application, perhaps until such time that a more extensive range of laboratory spectral lamps, the LL series, was introduced around 1950.

A single cathode is mounted at the centre of the bulb and is coated with barium oxide for good electrode emission. The discharge is struck to a pair of ring-shaped molybdenum anodes each spaced a few centimetres above and below the cathode. The discharge length is so short that this lamp could probably have been used on either DC or AC supplies.

A conventional flare and stem design is employed to seal the bulb. To prevent the condensation of sodium in the cool neck and maintain a sufficiently high vapour pressure, this portion of the bulb is sealed off with a mica plate cemented into the neck. The disc is pierced by a small ceramic tube, and this presents a sufficiently long and tortuous path that it is quite effective in preventing sodium diffusing into the lower void where it would otherwise attack the seals. The lamp is intended for operation within a dewar jacket to provide the necessary degree of thermal insulation, raising the temperature for optimum sodium vapour pressure.
Manufacturer: N.V. Philips Gloeilampenfabrieken
Lamp Power: c. 30 Watts?
Lamp Current:
Lamp Voltage:
Cap Type: 4-Pin Valve Bakelite
Bulb Type: T-38 mm T-12 eighths/inch
Bulb Finish: Clear Borate Glazed Soda-lime
Electrodes: Coiled-Coil tungsten BaO emitter
Arc Length: 2 x 20mm 2 x 0.75 inches
Atmosphere: Na 0.5 grams Neon 1.5 torr
Luminous Flux: c. 500lm
Luminous Efficacy: c. 17 lm/W
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: Unknown
Warm-up & Re-strike Time: c. 5 minutes Instantaneous
Burning Position:
Overall Length: 150mm 6 inches
Light Centre Length: 120mm 4 inches
Factory: Eindhoven The Netherlands
Date of Manufacture: c. 1940
Original & Present Value: Unknown
References: 1) Low Voltage Sodium Vapour Lamps,
2) Catalogue of the Historic Lamps, Philips Eindhoven Collection, c. 1950.
3) "The Sodium Lamp : From Lab Experiment to Street Lighting", E.G. Dorgelo & P.J. Bouma, Philips Tech. Rev. Dec. 1937 V.2 No. 12 pp.354-360.
4) "Operating Characteristics of Sodium Vapor Lamps", Dr. N.T. Gordon, GE Review July 1934 V.37 No.7 pp.338-341.
5) "Natrium en Kwiklampen", C.T. Haverkorn van Rijsewijk en H.C. Van Der Molen, Publ. NV Uitgevers Maatschappij Diligentia, Amsterdam, 1950.
6) "SOX Lamps Break 200lm/W Barrier", Electrical Review November 1982, V.211 No.16 pp.25.