GE Lucalox High Pressure Sodium Prototype

Presented here is a very early HPS lamp whose appearance is almost identical to the first commercial model of 1965. Electrically it is unusual because of its high arc voltage and low current, which may imply that it is a lab sample of the co-inventors Kurt Schmidt and William Louden.

The arc tube is made of transLUCcent ALuminium OXide (LUCALOX), whose ends are thickened to increase strength. Deep-drawn niobium thimbles are sealed over the ends using a glassy frit interface. The thimbles are penetrated by niobium tubes, the inner ends of which are TIG-welded to the electrode shanks. The outer end of one of these tubes is used to fill the arc tube via small holes in the side of the inner part of the tube (see X-Ray), before being pinched-off outside. The electrodes are recessed into the thimbles to prevent formation of a cold spot, and the sodium amalgam resides inside the arc tube. Incidentally the proximity of the electrodes to the seals was found to cause short life due to the high temperature of the frit seals which reacted with the sodium fill, and the HPS lamp was redesigned in 1967 to feature short metal cups far away from the electrodes, and an external amalgam reservoir. The electrodes are coated with barium thorate emitter material, which was replaced by dibarium tungstate in 1970 to further extend life.

The arc tube is mounted on a support frame borrowed from the company's mercury lamps, with a spiral of braided wire at one end to absorb thermal expansion of the ceramic arc tube. A nickel plated steel heat-reflector disc serves to keep the cap temperature as low as possible. The outer envelope is evacuated to reduce heat losses, but curiously does not employ the usual barium getters to maintain high vacuum.
Manufacturer: General Electric Company U.S.A.
Lamp Power: Approx. 500 Watts
Lamp Current: 2.5 Amps
Lamp Voltage: 250 Volts 2500V ignition
Cap Type: E39s/41 Brass + vitrite
Bulb Type: BT-117 BT-37 in eighths/inch
Bulb Finish: Clear Lead borosilicate glass
Electrodes: Double tungsten coils BaThO3+0.1Th Emitter
Arc Length: Approx. 70 mm
Atmosphere: Inner: Na,Hg | Xe Outer: Vacuum
Luminous Flux: Approx. 50,000 lm
Luminous Efficacy: Approx. 100 lm/W
Colour Temperature & CRI: CCT: 2100K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.512 CCy: 0.420
Rated Lifetime: Approx. 3000-6000h
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Universal
Overall Length: 292 mm 111/2 inches
Light Centre Length: 178 mm 7 inches
Factory: Cuyahoga, NELA Park Cleveland OH, U.S.A.
Date of Manufacture: Circa 1965
Original Value: No commercial value
References: 1) High Pressure Sodium Discharge Arc Lamps, W.C.Louden & K.Schmidt, Illuminating Engineering, December 1965, pp.696-702
2) US Patent 3,243,635, Ceramic Lamp Construction, W.C.Louden & R.S.Pinter (General Electric), filed Dec. 1962
3) US Patent 3,248,590, High Pressure Sodium Vapor Lamp, K.Schmidt (General Electric), filed Mar. 1963