The light-guiding optical system comprises at least one light source (2) and a light guide (1) for coupling and guiding light rays (10) emitted by a light source (2). Furthermore, the light guide (1) may comprise a decoupling surface (4) on its rear side (13) and an output surface (3) for the exit of light rays (10) decoupled by the decoupling surface (4) on an opposite front side (14). The decoupling surface (4) comprises: (i) first decoupling elements (5) configured to decouple light rays (10) falling onto the first decoupling elements (5) out of the light guide (1) approximately in a pre-determined first output direction (p) to fulfill a first light function, and (ii) a second decoupling element (6) configured to uncouple light rays (10) falling onto the second decoupling elements (6) out of the light guide (1) approximately in a pre-determined second output direction (d), which is deflected from the first output direction (p), to fulfill the second light function.