| 摘要 |
PURPOSE:To improve a starting property and a luminous flux maintenance rate for obtaining a long life by forming at least one of an electrode axis and a coil mounted thereon of an iridium Ir - tungsten W alloy while specifying the contents of Ir in the alloy. CONSTITUTION:A pair of electrodes 3A, 3B and an auxiliary electrode for starting 3C are connected to the external leading wires 5A-5C through the metal foils 4A-4C for sealing respectively while a proper quantity of rare gas for starting, for example, argon gas and mercury are sealed inside a tube. A coil 7 in which an electrode axis 6 made of an Ir-W alloy wire having the Ir contents of 1% weight ratio is wound round with a tungsten wire is mounted on the electrodes 3A and 3B, while the coil 7 is coated with an electron discharging material 8 consisting of, for example, alkaline earth metal oxides BaO, CaO and a high melting point oxide Y2O3. Since an operation temperature of the electrodes 3A and 3B is lowered, evaporation and scattering of the electron discharging material 8 are decreased, thereby being able to suppress down a drop in a starting property and a luminous flux.
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