Brewster's angle

Summary

Brewster's angle is the angle of incidence at which light polarized in the plane of incidence is not reflected at all. The reflection takes place at a flat interface between two transparent media. For light going from index $n_1$ to index $n_2$ it equals $\arctan(n_2/n_1)$. Unpolarized light reflected at this angle is therefore fully polarized perpendicular to the plane of incidence. It is used in polarizers, laser windows and glare-reducing sunglasses.