In an air-tight at least partially transparent container, a phosphor, a gas or gas mixture and a pair of discharging electrodes are contained. The discharge gap is in the range of 0.1 to 3.0mm, and the pressure of the gas or gas mixture sealed in the container is such that the product of the pressure and the discharge gap is in the range of 30 to 300 Torr.mm. The gas or gas mixture has discharge radiation spectra within the region of wavelength shorter than 200nm. The phosphor is a manganese activated aluminate phosphor represented by the formula(M.sup.II.sub.1-x, Mn.sub.x ) O.multidot.zAl.sub.2 O.sub.3where M.sup.II is selected from a group consisting of calcium, strontium, barium, magnesium and zinc, and x and z are numbers within the ranges of 10.sup.-3 .ltoreq.x.ltoreq.7.times.10.sup.-1 and 1.ltoreq.z.ltoreq.20, respectively.