A light-generating unit includes at least one light source group and a power supply module. The light source group includes a plurality of light sources each emitting a light of a different color from each other and each having a different effective light-emitting area from each other, so as to generate a white light including a mixture of lights emitted from the light sources. The power supply module applies one driving voltage to the light sources. Thus, a white light having a desired wavelength distribution may be generated while one driving voltage is applied to the light sources of the light-generating unit.