GE LU50/A - First American Medium-Based HPS
Following the introduction of the first HPS lamps of 400W, there was strong market demand for lower powers. This was no easy challenge, as it becomes more difficult to maintain long life and high efficacy in smaller discharge lamps. Every few years a lower wattage joined the range, but it took well over a decade before 50W became feasible - appearing between 1977 and 1979. The first model was in a large ED23½ bulb with mogul base. This particular lamp of 1980 was the first compact version with a medium screw base.

At first it was believed that this 50W medium-based lamp would replace incandescent lamps, hence the use of a pear-shaped A23½ bulb. This is made in hard glass to protect it from rain. Within a year though it has been abandoned, in favour of a smaller ellipsoidal B17 shaped outer envelope.

It is notable that for the early 50W and 35W lamps, GE departed from its classic arc tube with external amalgam reservoir. At such low powers that would represent a large heat sink, and cool the tiny 50W electrodes too much, impairing lamp efficacy and life. Instead the arc tube ends are closed with alumina plugs pierced by thin niobium-zirconium wires, the whole being sealed with a glassy frit. A bow-shaped niobium wire serves to hold the electrode and plug assembly during sealing, and acts as a wick to evenly distribute the sealing glass. A major drawback of this seal is that some of the frit glass penetrates along the seal into the arc tube - where it is undergoes a chemical reaction that leads to sodium loss, rapid voltage rise and short life. This problem was only overcome around the end of 1985, by which time GE's external amalgam reservoir design had successfully been adapted for lamps as small as 35W.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 50 Watts
Lamp Current: 1.18 Amps
Lamp Voltage: 52 Volts
Cap Type: E26s/25 Brass + vitrite
Bulb Type: A-75 A-23½ in eighths/inch
Bulb Finish: Clear Lead borosilicate glass
Electrodes: Backwound Tungsten Ba2CaWO6 Emitter
Arc Length:
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 3,300 lm (@ 100 hrs) 2,970 lm (@ 12,000hrs)
Luminous Efficacy: 66.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1900K CRI: Ra 22
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 24,000 hours to 50% survival
Warm-up & Re-strike Time: 5 minutes approx 2 minutes
Burning Position: Universal
Overall Length: 138 mm 57/16 inches
Light Centre Length: 90 mm 31/2 inches
Factory: Ravenna, OH U.S.A.
Date of Manufacture: March 1980 Date Code: 3 ∙-
Original Value: Unknown
 
References: 1) General Electric USA Large Lamp Catalogue, Form 9200, 1979
2) US Patent 4,034,252, Ceramic Lamp Seal and Control of Sealing Frit Distribution, C.I.McVey (General Electric), filed Dec. 1975