The International Year of Light 2015 is a welcome opportunity to look back to observations and famous experiments that lead to revolutionary theories in physics around the phenomenon of light. The observed aberration of starlight and later the experiment of Michelson and Morley were in contradiction to the electrodynamic theory of light until the special relativity theory solved the conflict by proposing time and space effects in moving systems. Today, laser and CCD technlogies enable much more precise measurements than in former times. The most accurate test of electrodynamics is achievable by aberration measurement of a laser beam because it offers an effect in the first order of v/c. The results of the experiment verify the findings of Michelson and Morley but are, surprisingly, in contradiction to electrodynamics and to special relativity theory. Our picture of the light's properties is still imperfect.