An illumination can be generally understood as a light transformation where an input field is transformed into a specified output field. There are several approaches to achieve the desired illumination. These approaches differ with respect to the used concept as well as the realization done by the optical system. For illumination tasks the usage of diffusers is very promising. The concept and the
realization by an optical system are presented and discussed. The
functionality of a diffuser is not restricted to coherent light but it is also applicable to partially coherent light. This seems to be of special interest for illumination tasks. Beyond that, some experimental results of the usage of a non-paraxial diffuser in combination with a light emitting diode are presented.