GE NA-1 Sodium Vapour Lab-Arc

This lamp is a small version of the NA-9 10,000 lumen equivalent, which was once popular for American street lighting. The NA-1 was developed as a convenient source of monochromatic light for lab work - e.g. to demonstrate the classic Young's Slits experiment. It also had industrial applications in determining surface flatness, liquid flow etc.

The lamp is a short-arc low voltage type, similar to the earlier Philips DC Polarimeter lamp but for AC use. It requires preheating of the tungsten coil cathodes, before the discharge is struck in a neon-argon mixture and then carried by molybdenum anode plates. Instead of using 2-ply sodium-resistant glass, American sodium lamps are unusual in that they use ordinary borosilicate glass with an inner protective glaze of crystalline borosilicate. This shows excellent resistance to sodium, and can be recognised by the diffuse appearance. To protect the glass-to-metal seals, these are made in a lower bulb separated from the main discharge vessel by a mica plate sealed with ceramic paste. A glass tube connects the two bulbs, its diamter being narrow to reduce the mean free path of sodium atoms and reduce their rate of diffusion into the lower bulb. Sodium dosing was effected by exploding a small glass 'bomb' inside the main bulb during the exhaust stage. This had been previously filled with sodium under vacuum and was exploded by heating with an RF induction oscillator.

It must be operated in a heat-conserving dewar vacuum jacket. These were marketed along with a special luminaire and control gear by the George W. Gates laboratory supply company (type SLA-5C). Many lamps also bear a label as Gates type G5CL. They were discontinued in 1972.
Manufacturer: General Electric Company, U.S.A.
Lamp Power: 28 Watts
Lamp Current: Discharge 4.0 Amps Cathodes 2x 2.5 Amps
Lamp Voltage: Discharge 6.5 Volts Cathodes 2x 1.5 Volts
Cap Type: UX4 4-pin Valve
Bulb Type: TB-38 TB-12 in eighths/inch
Bulb Finish: Diffuse Borosilicate with glaze
Electrodes: Coiled-Coil Tungsten BaO emitter
Arc Length: 17.5 mm 11/16 inch
Atmosphere: Na | NeAr
Luminous Flux: 650 lm
Luminous Efficacy: 23 lm/W
Colour Temperature & CRI: CCT: 1800K CRI: Ra -43
Chromaticity Co-ordinates: CCx: 0.565 CCy: 0.430
Rated Lifetime: Approx 500 hours
Warm-up & Re-strike time: 15 minutes Instantaneous
Burning Position: Vertical cap down
Overall Length: 136 mm 53/8 inches
Light Centre Length: 82.5 mm 31/4 inches
Factory: Hokoken, N.J. U.S.A.
Date of Manufacture: July 1960 Date Code 54
Original / Present Value: Unknown
 
References: 1) "GE Lamp Bulletin", C.E.Weitz, May 1946.
2) "GE Special Lamps Catalogue", June 1968.
3) Photo-Electric Measurement in Gates SLA-5C Sodium Lab-Arc @ 120V 60Hz
4) "The AC Sodium Vapour Lamp (10,000lm Na-9)", G.R.Fonda and A.H.Young, General Electric Review, July 1934, pp.331-337.
5) "Operating Characteristics of Sodium Vapor Lamps", N.T.Gordon, General Electric Review, Jul 1934 pp.338-341.
6) "Low Voltage Sodium Vapour Lamps", Lamptech Museum of Historic Lamp Technology
7) US Patent 2,087,747, Thermionic Discharge Device, A.H.Young, General Electric USA, Filed 16th Nov 1932.
8) US Patent 2,030,380, Sodium Resistant Glass, L.Navias, General Electric USA, Filed 11th August 1934.