On the physical reality of edge sources

In the celebrated Sommerfeld's rigorous solution to the half-plane problem, a condition fully demonstrated states that the edge neither radiates nor absorb energy. So, the well known Grimaldi's phenomenon, the shining of the edge, is claimed as an “optical illusion” (literally optische Täuschung) in his original paper. This paper deals with an apparent contradiction about this matter showing experimentally that the edge acts as a real source.