Display screens used for digital watches and most portable computers are Liquid Crystal Displays (LCDs). LCD displays have two sheets of polarizing material. These sheets are separated by a liquid crystal solution. An electrical current passing through the liquid causes the crystal to align allowing or preventing light from passing through. Therefore LCD screens can be lightened or darkened by applying/removing current. Nearly all modern flat-panel displays use LCD technologies, although new technologies such as the amazingly realistic OLED screens are poised to take their place in the near future.