| 摘要 |
PURPOSE:To avoid the dielectric breakdown of a ballast or the like due to surge voltages, by filling mercury in the outer tube of a metal vapor discharge lamp equipped with a luminous tube and starting thermoresponsive element and allowing the thermoresponsive element to function in an atmosphere of the vapor of mercury. CONSTITUTION:In an outer tube 7 of a high pressure sodium lamp or the like, there are provided a luminous tube 1 and a thermoresponsive element 4 such as a bimetal switch or the like. The luminous tube 1 and termoresponsive element 4 are connected to a power source 9 through a ballast 8. The lamp is started and lighted by using a pulselike high voltage which occurs at the ballast 8 spontaneously upon an opening of the contact of the thermoresponsive element 4. Mercury is filled in the outer tube 7 while controlling its filling gas pressure not higher than 20 Torr. Thus, a part of a surge voltage which is produced upon an actuation of the thermoresponsive element 4 is consumed through a discharge caused at the contact of the element 4. This avoids occurrence of any annecessary high voltages, thereby protecting the ballast 8 or the like from damages due to dielectric breakdown. |
