 Optical rotation or optical activity sometimes referred to as rotary polarization is the rotation of the plane of polarization of linearly polarized light as it travels through certain materials. Optical activity occurs only in chiral materials, those lacking microscopic mirror symmetry. Unlike other sources of pirate fringes which alter a beam's state of polarization, optical activity can be observed in fluids. This can include gases or solutions of chiral molecules such as sugars, molecules with helical secondary structures such as some proteins, and also chiral liquid crystals. It can also be observed in chiral solids such as certain crystals with a rotation between adjacent crystal planes such as quartz or metamaterials. Rotation of light's plane of polarization may also occur through the Faraday effect which involves a static magnetic field, however this is a distinct phenomenon that is not usually classified under optical activity. The rotation of the plane of polarization may be either clockwise, to the right next rotari, d-rotary or to the left leader rotari, l-rotary depending on which stereo isomer is present toward dominant. For instance, sucrose and camphor-hardy rotari were as close to a roll as l-rotary. For a given substance, the angle by which the polarization of light of a specified wavelength is rotated is proportional to the path length through the material and for a solution proportional to its concentration. The rotation is not dependent on the direction of propagation, unlike the Faraday effect where the rotation is dependent on the relative direction of the applied magnetic field. Optical activity is measured using the polarized source and polarimeter. This is a tool particularly used in the sugar industry to measure the sugar concentration of syrup and generally in chemistry to measure the concentration or enanti-americ ratio of chiral molecules in solution. The rotation of a liquid crystal in optical activity, viewed between two sheet polarizers, is the principle of operation of liquid crystal displays used in most modern televisions and computer monitors.