A light radiator is described which is capable of being threadably attached to the light-emitting end of a fiber optic cable to radiate light rays transmitted therethrough. The light-guide rod has a thread at a circumference of its one end in order to be threadably connected to the light-emitting end of the fiber optic cable and the light-guide rod has a spiral groove at its circumference. The spiral groove gradually getting deeper as it approaches the rod's tip in order to diffusively radiate the light therefrom.