PURPOSE: To minimize infrared radiation and maximize visual light radiation, by making up a radiation means out of an array of cavities of a certain substance and adapting the size of the cavities to allow this substance to transmit only electromagnetic radiation with wavelengths longer than a predetermined value.

CONSTITUTION: This device is equipped with a plurality of separate xenon radiation sources 10 disposed in oblong, square cross-section waveguide cavities 12, and each cavity is formed of side face members 14A to 14D each having a lateral size of 350 nm and a length of 700 nm. Each waveguide cavity 12 has a cut-off wavelength of 700 nm without a mode for radiating wavelengths longer than 700 nm. Electron transition of discharge plasma, causing infrared radiation with a wavelength of 700 nm or longer in free space, is thereby prevented from being generated in waveguide cavity discharge. Infrared radiation can be prevented and luminousity is improved.