||This lamp is representative of the second model of high pressure sodium lamp to have been manufactured in Hungary, by that country's state-run lampmaker, Tungsram. It is believed to date to the mid or late 1970s, since it was removed from streetlighting service on the streets of Budapest in 1980. The arc tube end seals are of a particularly interesting construction unique to Tungsram.
The seals have been formed to discs pressed from niobium metal (not visible), having a first large cup-shaped depression that contains the end of the arc tube, and a second depression that protrudes beyond the end of the arc tube. They are believed to have been fused to the ceramic arc tube with a glass frit material. Additionally a large ceramic washer of sintered alumina has been frit-sealed to the outer surface of the arc tube. The arc tube is most unusually connected to the metal support frame of the outer envelope by sandwiching it between a pair of metal springs.
This lamp differs from Tungram's first generation design in that the large PCA cylinders were not used at first, and the metal cups were therefore of much smaller diameter. The design is believed to have been changed in an effort to extend lamp lifetime. Since there is no large cold spot to contain the sodium amalgam, it would be close to the delicate end seals which would be rapidly attacked by this corrosive filling. The large PCA cylinders were possibly added as a heat reservoir to raise the ceramic temperature at the ends, and the reason for the heavy-metal spring coils pushed against the niobium caps is possibly to provide a thermal gradient to force the sodium amalgam to condense there, away from the frit seals.