Polarised Illumination

Optical Illumination Technique - Transmitted and Polarised Lighting

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

Schematic of a polarising filter
The light that travels in the same direction as the crystal transmits through the filter.
The light that travels in a different direction from the crystal can’t transmit through the filter.
Direction of transmission
Polarising filter
Polarised illumination image samples
Laminate-coated paper (30×)
Standard illumination
Polarised illumination