What is light? A correct answer to this question is: I don't know, but I can see some of its properties"! It is exciting to study such a complex thing and to search for models which can help us to try to understand, in a proper way, some of the most interesting behavior of light. We see the sunshine and the radiation makes us warm, undoubtly it must be some kind of energy? Interference experiments with monochromatic light show that the radiation has wave-like properties, but for example scattering experiments predict a particle nature. Maxwell showed (1865) that light could be an electromagnetic wave and he also wrote down, f priori, the correct velocity of propagation in vacuum. Planck and de Broglie established the simple connection between energy and frequency, and momentum and wavelenght respectively. The development of the quantum mechanical formalism started by Schrodinger and continued by Dirac~ was a signal for an explosion of ideas explaining an overwhelming number of physical phenomena.