| 摘要 |
PROBLEM TO BE SOLVED: To provide a fluorescent lamp expected for an improvement effect of brightness and luminous efficiency, and capable of providing fixed productivity, although the diameter of a circular glass tube is reduced. SOLUTION: This circular fluorescent lamp is made up of a circular glass tube 11 having electrodes 10, 10 disposed in both end parts thereof, and mercury and inert gas sealed therein. A recessed part 13 comprising a helical groove 13a partly recessed toward the inside of the glass tube is formed in a glass-tube outer circumferential surface including the middle part and distanced from both the end parts of the circular glass tube 11.
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