| 摘要 |
PURPOSE:To completely prevent the breakage of the emitter tube which might occur when an overcurrent flows by correlating the prearching time-current characteristic of a fuse installed in the feed circuit of the emitter tube with the inner diameter and the thickness of the emitter tube and using a fuse in which a current with at most a specified density flows during rated lighting. CONSTITUTION:A starting device 22 and an emitter tube 5 made of a light- transmitting ceramic member are installed in an outer tube 1. A fuse 21 which is fused by an overcurrent is connected to the feed circuit of the emitter tube 5 in series. The fusing current for the fuse 21 I(A), the time required for fusing the fuse 21 T1(sec), the inner diameter of the emitter tube 5 D(mm.) and its thickness t(mm.) are adjusted according to the formulae logT1<AlogI+B, A=-4.4X10<-3> (D<2>t)-2.46 and B=1.25X10<-2>(D<2>t)+5.01. Furthermore, the density of current flowing in the fuse 21 during rated lighting is adjusted to be at most 24.8A/mm.<2>. Consequently, even when an overcurrent flows in the emitter tube 5, it is possible to safely use the lamp until the last stage of its service life by completely preventing the breakage of the emitter tube 5. |
