A phosphor device of an illumination system emitting a first color light in a first waveband region includes a first region having n sub-regions and n single-powder phosphor agents, wherein n is ≧2. The n single-powder phosphor agents are coated on the n sub-regions, respectively, for transforming the first color light in the first waveband region into n color lights in n waveband regions. The n sub-regions are arranged in a specific area ratio. The first color light in the first waveband region is cyclically transformed into a second color light in a second waveband region, a third color light in a third waveband region, . . . , and a (n+1)th color light in a (n+1)th waveband region in a specific time ratio according to the specific area ratio, such that the n color lights sequentially outputted in the specific time ratio are integrated as a specific color light.