PURPOSE: To make light distributing characteristic uniform by forming a slit portion by means of a phosphor coating, lessen the width of an external electrode than the slit portion, and lessen the meandering width of a positive column so as not to bulge out of the width of the slit portion.

CONSTITUTION: A phosphor coating 2 having a slit portion 7 and a pair of internal electrodes 3a, 3b are provided inside a tubular bulb 1, and rare gas is filled thereinto. Outside the bulb 1 an external electrode 5 for drawing a positive column A to its bulb wall, and the width of the electrode 5 is formed so as to be narrower than the width of the slit portion 7. When high frequency power is applied to the electrodes 3a, 3b, the coating 2 is excited by a ultra-violet wave emitted from the positive column A so that light is emitted from the slit portion 7. Although the positive column A is drawn to the electrode 5 during its lighting, the meandering width of the positive column A becomes narrow so as not to be allowed to bulge out of the width of the slit portion 7 as the width of the electrode 5 is narrow. The slit portion 7 is formed of the coating 2 so that light distributing characteristic in an axis direction can be uniformed without forming the coating specially.