One of the most interesting problems in the illumination research community is the design of optics able to generate prescribed intensity patterns with extended input sources. Such optics would be ideally applied to the current generation of extended, high-brightness, high-CRI LEDs used in general illumination, allowing reduced size of luminaires and improved efficiency. But in 3D, for non-symmetric configurations, how to design optics for prescribed intensity using extended sources remains an open question. We present an alternative approach to this problem, for the case of extended Lambertian sources, in which the design strategy is based on the definition of selected “edge wavefronts” of an illumination system. The extended emitter is represented by input wavefronts originating from selected points belonging to its edge; the prescribed intensity pattern, instead, is put in relationship with specific output edge wavefronts. The optic is calculated by requiring that it transforms the input edge wavefronts exactly into the output ones. This wavefront-matching procedure can be achieved, for example, with the Simultaneous Multiple Surfaces method (SMS). We show examples of freeform optics calculated according to the above procedure, which create non-rotationally symmetric irradiance patterns out of extended sources. A fine tuning of the output design wavefronts allows accurate control over the uniformity and extension of the output patterns, as well as on the definition of cut-offs and intensity gradients.