An illumination system for a medical technology therapy and/or diagnosis system is provided. The system includes a light source, an optical waveguide, and an optical element in the form of a diffuser element. The optical waveguide has a first end that is connectable or assignable to the light source and the diffuser element is arranged at a second end of the optical waveguide so that light from the optical waveguide is injected into the optical element. The optical element has a lateral surface covered by a reflector layer at least in a section thereof. The reflector layer includes a mirror layer. The optical element has a light-reflecting area covered by the reflector layer and a light-transmissive area that is free of the reflector layer. Thus, light injected into the optical element is reflected on the light-reflecting area and emitted from the light-transmissive area.