TUBULAR BULB

PURPOSE:To prevent production of cracks, cuts, and other flaws by forming concave parts in bulb seal parts corresponding to positions where parted moulding dies are combined so as to restrict the height of protrusions of combining marks not to exceed the maximum diameter part of the seal parts. CONSTITUTION:In seal parts 3, combining mark protrusions 13, 13 to be produced when parted moulding dies 21, 22 of a moulding die 20 are combined are formed in concave parts 12, 12, and the protruding height of each protrusion 13 is set to be smaller than the maximum diameter part R in the seal part 3. In applying a cap 4, it can be applied smoothly because the protrusion 13 is not larger than the inner diameter of a cap shell 5. After the cap 4 is engaged, the protrusion 13 is not applied to the shell 5, so concentration of stress by addition of local pressure by pushing force of the shell 5 is eliminated. Production of cracks from the protrusions 13 or breakage of the bulb in applying process of the cap 4 or by repeated lighting and lighting off the lamp can thus be prevented.