ABSTRACT
The nature of light is one of the most difficult concepts in modern physics. Because of its quantum nature, light has to be considered in some experiments as an electromagnetic wave and in others as a particle. The different manners in which the fields change direction along the light trajectory are called polarization states. It is shown in any physical optics textbook that any polarization state may be considered as a superposition of two mutually perpendicular plane-polarized light beams. Light waves with different frequencies have different colors, corresponding to certain wavelengths in the vacuum. In lens design, the frequencies for the solar Fraunhofer lines are used to define the color of the light. An optically transparent medium is said to be homogeneous and isotropic if the light travels at the same speed in every direction inside the medium, independently of the orientation of the electric field.
