An illumination system, comprising: a light source , emitting a light beam (B, BA, BB); a first lens element , disposed on a transmission path of the light beam (B, BA, BB) emitted from the light source , wherein the first lens element has a curved surface (SC) and a multidirectional-plane (SM), the multidirectional-plane (SM) and the curved surface (SC) are disposed opposite to each other, and the multidirectional-plane (SM) comprises a plurality of sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) facing different directions; and an optical wavelength conversion module , disposed on a transmission path of the light beam (B, BA, BB) transmitted from the first lens element , wherein the optical wavelength conversion module converts a first portion (B1) of the light beam transmitted from the first lens element into a converted light beam (C), and the converted light beam (C) and a second portion (B2) of the light beam (B) transmitted from the first lens element form an illumination beam (IB); wherein the sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) comprise a plurality of first sub-planes, and the first sub-planes are respectively formed by rotating a reference plane (RF) perpendicular to an optical axis (OA) of the illumination system by different angles along a first midline (M1) of the multidirectional-plane (SM); and wherein the sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) further comprise a plurality of second sub-planes, and the second sub-planes are respectively formed by rotating the reference plane (RF) by different angles along a second midline (M2) of the multidirectional-plane (SM). a light source , emitting a light beam (B, BA, BB); a first lens element , disposed on a transmission path of the light beam (B, BA, BB) emitted from the light source , wherein the first lens element has a curved surface (SC) and a multidirectional-plane (SM), the multidirectional-plane (SM) and the curved surface (SC) are disposed opposite to each other, and the multidirectional-plane (SM) comprises a plurality of sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) facing different directions; and an optical wavelength conversion module , disposed on a transmission path of the light beam (B, BA, BB) transmitted from the first lens element , wherein the optical wavelength conversion module converts a first portion (B1) of the light beam transmitted from the first lens element into a converted light beam (C), and the converted light beam (C) and a second portion (B2) of the light beam (B) transmitted from the first lens element form an illumination beam (IB); wherein the sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) comprise a plurality of first sub-planes, and the first sub-planes are respectively formed by rotating a reference plane (RF) perpendicular to an optical axis (OA) of the illumination system by different angles along a first midline (M1) of the multidirectional-plane (SM); and wherein the sub-planes (P1, P2, P11, P12, P13, P14, P21, P22, P23, P24) further comprise a plurality of second sub-planes, and the second sub-planes are respectively formed by rotating the reference plane (RF) by different angles along a second midline (M2) of the multidirectional-plane (SM). <EOS>