Optical property in which a single ray of unpolarized light (seepolarization) splits into two components traveling at different velocities and in different directions. One ray is refracted (seerefraction) at an angle as it travels through the medium, while the other passes through unchanged. The splitting occurs because the speed of the ray through the medium is determined by the orientation of the light compared with the crystal lattice of the medium. Since unpolarized light consists of waves that vibrate in all directions, some will pass through the lattice without being affected, while others will be refracted and change direction. Materials that exhibit double refraction include ice, quartz, and sugar.