GE NA-9 Low Voltage AC Sodium

Within two years of the commercialisation of the first LPS lamps in Europe, GE developed its own version for the American market. This was an improvement over Philips' original 4000-lumen DC lamp, offering increased flux and efficacy, and being suitable for use on 6.6-amp AC circuits.

The small Philips DC lamps could not be scaled up to larger sizes owing to problems of sodium migration from anode to cathode. AC operation overcame this limitation and enabled the arc length to be increased by a factor of six even though the power was only doubled. The reduced current density assisted in giving this lamp a rather high efficacy. The longer arc meant that a positive column discharge was achieved, whose light generation efficacy is better than from the negative glow discharge in the vicinity of the electrodes.

The cathodes consist of tungsten coils at the centre of hemispherical bulb ends, surrounded by molybdenum rings which act as anodes. Ignition is facilitated by a third auxiliary electrode near the base, connected via a high resistance in the neck area. GE lamps feature a unique type of sodium-resistant discharge vessel. Instead of using 2-ply glass as in all other lamps, ordinary borosilicate bulbs are employed, with the inner surface being protected by a glaze of the same material but this being crystalline rather than glassy in nature. This gives the bulb a diffuse appearance. Crystalline borosilicate shows excellent resistance to attack by sodium, whereas in glassy state it would be destroyed quickly. A mica disc keeps sodium vapour away from the neck region, and the glass-to-metal seals are protected with a ceramic paste. A stack of soft asbestos washers around the neck provides a draught-free seal to the dewar jacket.
Manufacturer: General Electric Company, U.S.A.
Lamp Power: 190 Watts @ 0h 220 Watts @ 1000h
Lamp Current: Discharge 6.6 Amps Cathode Heating 10 Amps
Lamp Voltage: Discharge 25 Volts Cathodes 1.85 & 2.85V
Cap Type: UX4 British 4-pin Valve
Bulb Type: TD-76 TD-24 in eighths/inch
Bulb Finish: Diffuse Borosilicate with glaze
Electrodes: Coiled-Coil Tungsten BaO emitter
Arc Length: 230 mm 9 inches
Atmosphere: Na | Ne 1.5 torr
Luminous Flux: 12,000 lm @ 0h 10,000 lm @ 1000h
Luminous Efficacy: 63 lm/W @ 0h 45 lm/W @ 1000h
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: Approx 2,000 hours 50% suvival & 70% flux
Warm-up & Re-strike time: 5 minutes Instantaneous
Burning Position: Horizontal
Overall Length: 400mm 153/4 inches
Light Centre Length:
Factory: Nela Park, Cleveland U.S.A.
Date of Manufacture: November 1952 Date Code 59
Original / Present Value: Unknown
 
References: 1) The AC Sodium Vapour Lamp (10,000lm Na-9), G.R. Fonda and A.H. Young, General Electric Review July 1934 pp.331-337.
2) Operating Characteristics of Sodium Vapor Lamps, N.T. Gordon, General Electric Review Jul-34 pp.338-341.
3) Low Voltage Sodium Vapour Lamps, http://www.lamptech.co.uk/Documents/SO%20History%20LV.htm