| 摘要 |
PURPOSE:To cause no loss of transparency and generation of a crack in a luminous tube when lighting with power supply having no inversion of polarity such as a direct current by forming a cathode of a sealed axis and a discharge electrode and forming a coiled part on an end either of said sealed axis or the discharge axis to insert an end of the other into said coiled part for being engaged with it in order to be connected each other. CONSTITUTION:A cathode 3 is separated into a discharge axis 5 and a sealed axis 6 for being connected at a coiled part 7. Therefore, even when an arc is generated at the root part of the cathode at a starting time, both of mass and thermal capacity of the discharge axis 5 are small and moreover a calorie to be transmitted to the side of the sealed part 6 through the coiled part 7 becomes smaller because of the small contact surface of the coiled part 7 to the sealed part 6, thereby the temperature at the end part of the discharge axis 5 rises rapidly to the temperature at which an arc is easily generated. And with passing into a stable lighting state a metal inside a luminous tube 1 vaporizes so as to raise vapor pressure while the arc intends to shorten its distance as much as possible so as to finally turn to both electrodes 3 and 4. At a time of stable lighting the root part of the cathode 3 lacks in a spot for generating the arc thus obtaining a long life.
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