The science of determining the polarization state of electromagnetic radiation (x-rays, light or radio waves). Radiation is said to be linearly polarized when the electric vector oscillates in only one plane. It is circularly polarized when the x-plane component of the electric vector oscillates 90° out of phase with the y-plane component. In experimental work, the polarization state is usually expressed in terms of the Stokes parameters I (the total intensity of the radiation), Q (the preference for light to be linearly polarized in the x plane or at 0° in the instrument reference system), U (the preference for linear polarization at 45°), and V (the preference for left-circular polarization). When Q/I = 1, for example, the radiation is 100% linearly polarized along an axis at 0°. Similarly, V/I = −1 means that the light is 100% right-circularly polarized.