RLOD#22 (2020.05.28) 1980 GEC HPS/U 120W

Introduced in 1974, the HPS/U 120W shown here is the first European low-wattage high-pressure sodium lamp. Developed by GEC of England, it was initially designed to retrofit 125 W mercury lamps in order to facilitate market acceptance, but the British eventually had to release a dedicated 120 W series-choke ballast better suited to the lamp’s higher operating current (1.40 vs 1.25 A) and ignition requirement (1+ kV pulse). This HPS/U lamp has a design typical of early sodium lamps, featuring a cap-sealed burner with an external Hg-Na amalgam reservoir, and a built-in thermal starter for the discharge's ignition. In order to ensure a suitably long service life of 10 kh, GEC opted for a low operating temperature, which also resulted in rather mediocre performances for its wattage (71.7 lm/W initial). Competing low-wattage lamps that were released later during the 1970s (in 150, 70, and then 50 W) were much better optimized and became standard. The HPS/U 120W thus remained a GEC-specific lamp, whose production eventually ended in 2000 following the closure of the company’s Shaw factory in England (taken over by Osram of Germany in 1990).