Light emitting diode devices are improved remarkably in terms of light emitting efficiency and are free from mercury which is a toxic substance, whereby use thereof for illumination instead of conventional fluorescent lamps has energetically been studied in recent years. It is preferred that an illumination source emits a light having a spectral distribution close to that of sunlight. Thus, it is preferred that the illumination source has a flat spectral distribution containing components with every wavelength in the optical region. As white light source using light emitting diode devices, those obtained by a combination of three light emitting diodes for red, green, and blue emission or a combination of a light emitting diode for blue to ultraviolet emission and a photoluminescent material which absorbs the light emission, to thereby emit light from red to green, have been used. Examples of the former include so-called a three-in-one LED light source in which LEDs for red (AlInGaP), green (InGaN) and blue (InGaN) are included in one unit, and examples of the latter include a light source in which an InGaN-based blue LED and a so-called YAG fluorescent material to absorb a blue light to thereby produce a yellow fluorescence are combined.