Polarized light, or plane light, is light that vibrates within a single plane (“plane of vibration”) which is defined as the plane parallel to the ray’s path and its vibration direction. The polarized light results from the introduction of a single polarizing device into the optic path of a petrographic (polarized light) microscope, with the plane of vibration obtained from the privileged direction of the polarizer.
See petrographic microscope. Abbr. PL, or PPL (plane polarized light).