Polarized Illumination

Optical Illumination Technique - Transmitted and Polarized Lighting

A polarizing filter is an oriented crystal that transmits only the light that travels in a fixed direction. Polarized light doesn’t keep its polarization when it diffusely reflects.
However, when polarized light specularly reflects, it keeps its polarization. Using this principle, it is possible to use a polarizing filter, with adjustable orientation, to remove specularly reflected light.

Schematic of a polarizing filter

The light that travels in the same direction as the crystal transmits through the filter.

The light that travels in the same direction as the crystal transmits through the filter.
A : Light　B : Direction of transmission　C : Polarizing filter

The light that travels in a different direction from the crystal can’t transmit through the filter.