Optical rotation is the property of substances, rotating the plane of polarization when linearly-polarizedlight passes through such substances. This is the property which occurs specifically to optical activesubstances in which the refractive indices of right and left circularly-polarized light are different. Opticalrotation that rotate light in a clockwise direction as viewed towards the light source is defined asdextrorotation (+) and the opposite, levorotation (-).