Any liquid that has both a crystalline phase and liquid phase present at the same temperature. Liquid crystals are optically active and can split white light into two polarized components. This produces a double refraction or an iridescent effect. Many liquid crystals can also exhibit colors and even assume a succession colors, running through the spectrum from red to violet, as they are cooled or heated. Liquid crystals are used for electronic displays, thermometers and color TV tubes.