1979 GE LU50

GE of America was the first manufacturer to introduce a 50 W high-pressure sodium lamp on the market. The 50 W Lucalox released in 1977 featured an A-shaped outer jacket fitted with an E26 end cap, and a new wire-sealed burner which did not suffer from the thermal limitations that affected early HPS lamps made with the company’s signature external amalgam reservoir. The initial intention was to replace incandescent lamps in applications where light color is not critical. However, this plan did not work out due to too much differences in cost and characteristics between the two lamp technologies. Moreover, the 50 W sodium lamp was notoriously unreliable and its burner was prone to failure early in life.

The reliability issue was eventually solved in late 1979 when the burner construction was updated with GE’s 3rd-gen Lucalox design shown here and first released two years earlier in larger lamps. Improvements in the thermal design enabled the return of a small external reservoir, while the additions of metal foil wraps at the extremities of the arc tube limits end losses. Those heat shields also prevent the condensation of sodium in the seal areas, the primary cause of failure in the previous burner design. Those changes also resulted in the lamp’s initial output to increase by 21 % from 3300 to 4000 lm, thus making it a viable alternative to 100 W mercury lamps and to 207–295 W incandescent lamps that were commonly used to illuminate America’s secondary roads.

The LU50 in the form shown here was GE’s smallest full-sized Lucalox lamp made with the ED23.5 bulb and fitted with a mogul (E39) end cap. That particular lamp design replaced the original one in 1979 when it became clear that its main application would be in street lighting. Typical of US low-wattage sodium lamps, the LU50 has a low arc voltage of 52 V which enables an operation on 120 V mains circuits using a simple and economical series choke ballast. That particular choice in system design certainly contributed to the rapid adoption of this lamp in the early 1980s.