PURPOSE: To reduce power consumption by arranging an insulator on the way of discharge path in an enclosure thus increasing the discharge resistance.

CONSTITUTION: An insulator such as a glass tube 5 is arranged in longitudinal direction on the central axis connecting between the filament electrodes 4, 4 in an enclosure 1. The glass tube 5 has the hollow and cylindrical enclosed opposite ends held through holding tool 6 on the base metals 2, 2. Consequently, double structure of outside ring or the enclosure 1 and the inside rig or the glass tube 5 is realized where the area partitioned by the inside of enclosure 1 and the outside of glass tube 5 is employed as the discharge area while mercury drip and argon of several mmHg pressure are encapsulated in said area 7 and fluorescent material 8 is applied onto the inner face of enclosure 1. Since the discharge path is formed at the position near to the area applied with fluorescent material, ultraviolet beam absorbing efficiency is improved to maintain same illuminance with a fluorescent lamp having same diameter (a) resulting in reduction of power consumption.