LCD televisions produced a black and colored image by selectively filtering a white light. The light is provided by a series of cold cathode fluorescent lamps (CCFLs) at the back of the screen, although some displays use white or coloured LEDs . Millions of individual LCD shutters, arranged in a grid, open and close to allow the amount of the white light to pass through it. Each shutter is paired with a colored filter to remove all but the red, green or blue (RGB) portion of the light from the original white source. Each shutter–filter pair forms a single pixel. Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are perpendicular to each other. With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. Liquid crystals are a wide range of rod-shaped polymers that naturally form into thin layers, which is opposite if compared with the alignment of a normal liquid. Some of these, the nematic liquid crystals, also show an alignment effect between the layers. The particular direction of the alignment of a nematic liquid crystal can be set by placing it in contact with an alignment layer or director, which is essentially a material with microscopic grooves in it. When placed on a director, the layer in contact will align itself with the grooves, and the layers above will subsequently align themselves with the layers below, the bulk material taking on the director's alignment The underlying principle in a nematic liquid display is the manipulation of polarized light. When light enters the cell, the polarization state twists with the director of the liquid crystal material. The black lines represent crossed polarizers that are attached to the top and bottom of the display. As light enters the cell, its polarization rotates with the molecules. When the light reaches the bottom of the cell, its polarization vector has rotated by 90 degrees, and now can pass through the second polarizer. In a reflecting TN display, a mirror is placed at the bottom of the cell to reflect the transmitted light. Once again the polarization twists as the light traverses the sample, and is able to emerge from the top of the cell.
