Malus' law

In wave optics, Malus’ law describes how the intensity of linearly polarised light changes when passing through a linear polariser. It is given by:

$$I=I_0{\cos }^2\theta$$

where:

• $I$ is the intensity after the polariser.
• $I_0$ is the input intensity.
• $\theta$ is the angle between the light’s polarisation direction and the polariser’s transmission axis.