Polarizers: polarization by selective absorption

Another way to polarize light is by selectively absorbing light with electric field vectors pointing in a particular direction. Certain materials, known as dichroic materials, do this, absorbing light polarized one way but not absorbing light polarized perpendicular to that direction. If the material is thick enough to absorb all the light polarized in one direction, the light emerging from the material will be linearly polarized. Polarizers (such as the lenses of polarizing sunglasses) are made from this kind of material.

If unpolarized light passes through a polarizer, the intensity of the transmitted light will be 1/2 of what it was coming in.

If linearly polarized light passes through a polarizer, the intensity of the light transmitted is given by Malus' law:

I1 = Io cos2(q)

where q is the angle between the polarization direction of the light and the transmission axis of the polarizer.