What is the difference between S- and P-polarization?
S-polarization (the s stems from the German word senkrecht meaning perpendicular) and P-polarization (the p means parallel) are the two main ways to describe two types of linearly polarized light. A primary misconception when using the terms is assuming that P is always vertical and S is always horizontal. This is not true. P and S are relative to a surface (usually the surface that the light is acting upon and/or reflecting from). To properly define S- and P- polarizations, we first need to define the term plane of incidence. The plane of incidence is the plane that the incident and exiting beams lie in and is perpendicular to the surface that the light is incident upon. P-polarization refers to light that is polarized parallel to the plane of incidence. S-polarization refers to light that is polarized perpendicularly to the plane of incidence. So saying that P-polarization is always up-down and S is always side-to-side is incorrect. One example where this is incorrect is with a commo
