HIGH PRESSURE SODIUM LAMP

PURPOSE:To prevent any explosion of an emission tube by using as at least a part of an inner lead wire a conductor wire which has a fuse function and in which its sectional area is maintained in a relation with the starting rare gas charged in the emission tube in accordance to a specified inequality. CONSTITUTION:An internal lead wire 12 having a fuse function is formed by a conductive wire having a melting point of between 800 deg. and 2,000 deg.. When the sectional area of the conductive wire is supposed to be S(mm. ), the lamp current is supposed to be I(ampere) and the pressure of a starting rare gas charged in an emission tube 5 is supposed to be P(Torr), they are adjusted according to logP>= 0.4(I/S)+0.9. Owing to the above constitution, the internal lead wire fuses when an excessively large current flows in the lamp thereby preventing any explosion of the emission tube. Since the fuse function is restricted by the pressure of the starting rate gas charged in the emission tube, no cracks are formed in the emission tube.