When two pieces of Polaroid are placed in succession along the path of a light wave, the intensity of light received behind the two Polaroids is described by Malus’ Law. The law expresses light intensity, I, as a function of the angle which is the angle θ between the directions of polarization of the two filters. The law can be expressed as follows:
I = Imaxcos2 θ
where, Imax is the light intensity between the two sheets of Polaroid.