Malus' law (polarized light)

Description

A polarizer or polariser is an optical filter that passes light of a specific polarization and blocks waves of other polarizations.
When a perfect polarizer is placed in a polarized beam of light, the intensity of the transmitted part of the wave is proportional to the intensity of the the polarized wave before passing through the filter.
Malus’ law says that when a perfect polarizer is placed in a polarized beam of light, the intensity, I, of the light that passes through is depended on the initial intensity and the angle between the light’s initial polarization direction and the axis of the polarizer.
(The term intensity is used to describe the rate at which light
spreads over a surface of a given area some distance from a source. The intensity varies with the distance from the source and the power of the source).

Related formulas

Variables

IIntensity of the transmitted wave (W/m2)
I0The initial intensity (W/m2)
θiAngle between the light's initial polarization direction and the axis of the filter (degree)