Unsaturated vapor pressure type high pressure sodium lamp

摘要

In an unsaturated vapor pressure type high sodium lamp, a glass solder used for closely sealing a cap to fix to an arc tube includes a first component which is a mixture of Al2O3, CaO and Y2O3, and a second component including at least one of Sc2O3, La2O3, Sm2O3, Ce2O3, Yb2O3 and Dy2O3; and a constant percentage of the second component in the glass solder is in a range of 2 to 15 weight %.