Liquid Crystal Display is a kind of screen filled with a polarizing fluid between two glass plates. This liquid is an electrically controlled fluid trapped between two transparent polarizing sheets. The polarizing axes of the two sheets are aligned perpendicular to each other. The polarizing liquid is filled in cells which have electrical contacts to permit the entry of electrical field into the cells. When an electric field is applied, the molecules in the liquid align themselves with the field, inhibiting rotation of the polarized light. As the light hits the polarizing sheet perpendicular to the direction of polarization, all the light is absorbed and the cell appears dark.
The whole display has array of segments called Pixels which may be coloured or monochrome or both. The pixels may be divided into Sub pixels of Red, Green, and Blue by additional filters as in the case of LCD TV. These pixels are arranged in front of a light source with a reflector. Each sub pixel can be controlled independently to produce thousands or millions possible colors for each pixel. The liquid crystal makes the light to pass through the other by twisting the polarization of light entering one filter. By applying a small electric charge to transparent electrodes over each pixels or sub pixels, the molecules of the liquid crystal are twisted by electrostatic forces. This reorientation of the liquid crystal makes the image.
LCD screen is too sensitive to mechanical shocks and heat , since the pressure may squeeze the fluid present in between the plates which can cause its permanent damage. Excessive heat can change the physical properties of the liquid so some part of the screen may damage and appear as black spots or segments.