Linearly polarised light is composed of left and right circularly polarised partial light waves, with both components having equal amplitudes. When these partial waves propagate through the chiral material, they encounter different refractive indices due to the asymmetry of the medium. The partial wave that oscillates through a larger refractive index will travel slower than its counterpart, producing a phase difference between them. This phase difference causes the plane of polarisation to rotate. The angle of rotation caused by the differing refractive indices is described by the following equation:
Here, is the optical angle of rotation, and are the refractive indices of the left and right circularly polarised partial waves respectively, is the length of the optical path and is the wavelength of the light beam.
The rotation of linearly polarised light causes observable bright and dark bands to appear along the cell containing the solution because the light is not entirely observable from one angle.