Diffuser technology is known in diffractive optics for several decades and was mainly used together with coherent monochromatic light sources. In the last years diffusers play a more important role for illumination and homogenization task of partial coherent light sources, for example, Excimer lasers and LED's. In difference to illumination systems using lenses and micro lens arrays diffusers can be used to freely redistribute the intensity of the light source with a high homogeneity. Using diffuser technology for partial coherent illuminations needs an understanding of the characteristics of the light sources as coherence, wavelength bandwidth, divergence, radiation characteristic/intensity distribution. Since these characteristics are different for coherent and partial coherent light sources, these must be taken into account during the design of diffuser. This leads to new design concepts and surface structures. The authors will explain concepts of diffuser design for LED's and Excimer lasers and will show practical results.