| 摘要 |
PURPOSE:To improve a lumen maintenance factor without any decrease of optical output by setting a load on the tube-wall of a fluorescent lamp to more than 1.0 W/cm<2> and regulating a cation atomic ratio of lanthanum to cerium in a phosphor material in a range from 2 to 6. CONSTITUTION:A fluorescent lamp 9 is installed in the translucent globe 3 of a fluorescent lamp, the lamp 9 is formed approximately in a character b- shape and a phosphor material membrane 11 is formed on the whole inner surface of an emitting valve 10 in the lamp 9. Mercury is sealed in the lamp 9 in the form of amalgam, and lanthanum phosphate phosphor material activated by cerium and terbium (La, Ce, Tb)2O3.0.2SiO2.0.9P2O5 is employed in the phosphor material 11. A cation atomic ratio of lanthanum to cerium (La/Ce) is regulated in range from more than 1 to less than 6. Therefore, theris no decrease in optical output where a tube wall loading temperature is to be high with more than 1.0 W/cm<2> and its lumen maintenance factor can be improved.
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