<P> 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 birefringence 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 structure 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 ." </P> <P> The rotation of the plane of polarization may be either clockwise, to the right (dextrorotary--d - rotary), or left (levorotary--l - rotary) depending on which stereoisomer is present (or dominant). For instance, sucrose and camphor are d - rotary whereas cholesterol is 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 . </P>

How do you know if a product is optically active