Natural Radiation

Figure 16.1: The electric field in an ordinary light

What is the polarization state of the light from a natural source like the sun or from an incandescent lamp? Such sources may be thought of as a collection of a large number of incoherent sources. The radiation is the sum of the contributions from all of these sources. The electric field $\vec{E}$ of the resulting light wave varies randomly (Figure 16.1) in the plane perpendicular to the direction in which the wave propagates. This randomly polarized light is referred to as unpolarized light.