| 摘要 |
PURPOSE:To prevent development of cracks at the end of a luminescent tube by electrically isolating a proximity conductor to avoid contact with a heat insulating cover in a ceramic luminescent tube having a metallic heat insulating cover and a proximity conductor. CONSTITUTION:A metallic heat insulating covers 2 are set at both ends of a luminescent tube 1 used for a high pressure sodium lamp, and a proximity conductor 3 is arranged between both electrodes along the outer wall of the tube to perform lighting operation. The proximity conductor 3 is arranged so as to electrically isolate it from the heat insulating cover 2. Change in soldering material composition of sealing part which is caused by photo-electrons generated by applying potential to the heat insulating cover 2 until potential applied to the proximity conductor is cut by a bimetal switch is prevented, and development of cracks at the end of the tube are prevented. |
