Philora DO-80 AC Sodium Lamp

This lamp represents the first design of sodium lamp which could operate without the need for a continual current flow through its electrodes to maintain them at a satisfactory temperature for optimal efficacy. This greatly simplified the requirements of the electrical control gear and set the standard for all future low pressure sodium lamp designs, whose electrode construction remains virtually unchanged today. Towards the end of 1932 it superseded Philips' previous lamp design, the somewhat better known DA-90 whose construction was basically the same, the only major difference being the requirement for cathode heating.

The earlier DA-90 was a 90-watt lamp with approximately 10W being required to heat the cathodes. A special multi-pin cap enabled the electrodes to be independently heated. The power of this DO-80 lamp is lower on account of the fact that the electrode heating had been dispensed with. The cap was also simplified at this time to a simple E40 screw type. It is believed to have been introduced at the end of 1932, but this is difficult to confirm because it is not documented in any known literature. However this would seem likely since by the end of that year, it had itself been superseded by the SO family of low pressure sodium lamps.

Incidentally the 'D' in the name of these lamps refers to the fact that they have double-folded discharge tubes. 'A' signifies the original cathode design which required a continual heating current, while 'O' denotes the oxide-coated electrodes which are heated only by the discharge itself. The O-type cathode soon proved its superiority, and continued to be used in the single-folded (type S) discharge tubes in the SO series lamps which superseded this type later in 1932.
Manufacturer: N.V. Philips Gloielampenfabrieken
Lamp Power: 80 Watts
Lamp Current: 1.0 Amps
Lamp Voltage: 75 Volts
Cap Type: E40s Copper + Porcelain
Bulb Type: Inner: T-16 / Outer: T-80 Inner: T-6 / Outer: T-25
Bulb Finish: Clear 2-ply Borate on Sodalime
Electrodes: Triple Coil Tungsten BaO emitter
Arc Length: 450 mm 18 inches
Atmosphere: Na | 98.5% Ne, 1.5% Ar Outer: Vacuum
Luminous Flux: 4,000 lm
Luminous Efficacy: 50 lm/W
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: ca. 2000 hours
Warm-up & Re-strike time: 5 minutes Instantaneous
Burning Position: Vertical cap up
Overall Length: 175mm 7 inches
Light Centre Length:
Factory: Eindhoven Netherlands
Date of Manufacture: c. 1932
Original / Present Value: Unknown
References: 1) High 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) Elektrische Gasentladungslampen, W. Uyterhoeven, Julius Springer 1938, pp.216-218.