| 摘要 |
PURPOSE:To improve the maintenance factor of luminous flux, in a fluorescent lamp consisting of a long and narrow external tube enclosing rare gas and mercury and bended internal tubes housed in this external tube, by specifying the relation of the inner cross-sectional area of the external tube perpendicular to its axis and the outer diameter of the internal tube. CONSTITUTION:A long and narrow cylindrical external tube 1 contains internal tubes 2, 3, which are bended into a nearly U-shape, and also encloses mercury and rare gas air-tightly. The internal tubes 2, 3 have electrodes 6, 7 at their one ends respectively, and have openings 4, 5 at the other ends of them. When the inner cross-sectional area of the external tube 1 perpendicular to its axis is expressed as Scm<2> and the outer diameter of the internal tubes 2, 3 is expressed as Dcm, S and D are specified to satisfy the equation (S-piD<2>)/4piD<= 0.85. In this way, even when the lamp is lit up for a long time, the reduction of luminous flux can be minimized.
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