A bulb (5) for an electrodeless lamp system uses Sn or a halogenide of Sn as a primary bulb fill for obtaining a continuous spectrum (graphs ③, ④) when it is subjected to a discharge. The halogenide of Sn preferably is SnBr 2 . With such a fill, high photoefficiency and superior colour rendering can be obtained, and less ultraviolet rays than those (graph ②) produced by a sulfur fill are radiated, while a warm visual feeling can be obtained.