An illumination system configured to be included in a projection apparatus comprising a first light valve and a second light valve , the illumination system comprising: a first excitation light source configured to emit a first excitation beam (L1); a wavelength conversion element having a first region (R1) and a second region (R2) and comprising a wavelength conversion material in the first region (R1) and in the second region (R2), and a driving element to drive the wavelength conversion element to rotate around a rotation shaft so as to rotate the first region (R1) and the second region (R2) to sequentially enter into a transmission path of the first excitation beam (L1), wherein a concentration of the wavelength conversion material in the first region (R1) is greater than a concentration of the wavelength conversion material in the second region (R2), wherein the first excitation beam (L1) is transmitted to the first region (R1) in a first time interval (T1), the first excitation beam (L1) is configured to excite the wavelength conversion material in the first region (R1) to emit a first conversion beam (CL1), and the first excitation beam (L1) is transmitted to the second region (R2) in a second time interval (T2), a part of the first excitation beam (L1) excites the wavelength conversion material in the second region (R2) to emit a second conversion beam (CL2), and a different part of the first excitation beam (L1) passes through the second region (R2); wherein the first time interval (T1) and the second time interval (T2) are two consecutive time intervals; and a scattering element is disposed on the transmission path of the first excitation beam (L1) to be rotated with the wavelength conversion element synchronously, wherein the illumination system outputs the first conversion beam (CL1), a part of the second conversion beam (CL2), and the different part of the first excitation beam (L1) passing through the second region (R2) to the first light valve and the second light valve . a first excitation light source configured to emit a first excitation beam (L1); a wavelength conversion element having a first region (R1) and a second region (R2) and comprising a wavelength conversion material in the first region (R1) and in the second region (R2), and a driving element to drive the wavelength conversion element to rotate around a rotation shaft so as to rotate the first region (R1) and the second region (R2) to sequentially enter into a transmission path of the first excitation beam (L1), wherein a concentration of the wavelength conversion material in the first region (R1) is greater than a concentration of the wavelength conversion material in the second region (R2), wherein the first excitation beam (L1) is transmitted to the first region (R1) in a first time interval (T1), the first excitation beam (L1) is configured to excite the wavelength conversion material in the first region (R1) to emit a first conversion beam (CL1), and the first excitation beam (L1) is transmitted to the second region (R2) in a second time interval (T2), a part of the first excitation beam (L1) excites the wavelength conversion material in the second region (R2) to emit a second conversion beam (CL2), and a different part of the first excitation beam (L1) passes through the second region (R2); wherein the first time interval (T1) and the second time interval (T2) are two consecutive time intervals; and a scattering element is disposed on the transmission path of the first excitation beam (L1) to be rotated with the wavelength conversion element synchronously, wherein the illumination system outputs the first conversion beam (CL1), a part of the second conversion beam (CL2), and the different part of the first excitation beam (L1) passing through the second region (R2) to the first light valve and the second light valve . <EOS>