A light fiber and an illuminating device are disclosed. In an embodiment a light fiber includes a cladding and at least two cores configured to conduct electromagnetic radiation, wherein each core comprises an incoupling surface at one end of the light fiber, wherein the incoupling surfaces of different cores are not contiguous, wherein each of the cladding and/or the cores includes at least one outcoupling zone configured to outcouple the electromagnetic radiation from the cores, wherein the light fiber is configured to emit at least a majority of the electromagnetic radiation in a region of outcoupling zone transverse to a main extension direction of the light fiber, wherein the cores are configured to guide primary radiation, and wherein the outcoupling zone is configured to mix the primary radiation so that mixed light is emitted from the light fiber.