Light attracts painters, photographers, architects, and especially physicists and astronomers. This is an essay on the physical properties of light. We believe that the speed of light in vacuum is the same in all situations, which is difficult to grasp by reason. We have the feeling that light is understood by only a few individuals, however, this is not the case. Thus, let us unveil measurements and knowledge that shall illuminate the physical properties of light. In the first part of the book the author's view of the structure of light waves is described, while in the second part the methods of measuring the speed of light are analyzed by pointing out their strength and weakness. At the same time it puts forward suggestions for new measurements.