An optical arrangement for pre-processing primary illumination light is proposed, wherein a provided spectral processing section (P) comprises a multi-prism assembly (10) consisting of a plurality of sequentially/consecutively connected prisms (21, 22). Pairs (20) of adjacent and connected prisms (21, 22) form a respective spectral separating face (20c). The spectral separating face (20c) is adapted in order to perform a process of spectral separation/splitting with respect to said primary illumination light (L1).