An LCD is a device that uses these features in a surprising way.
To create an LCD, you need pieces of polarized glass( glass that make the light vibrations aligned into one or more planes of direction). A special polymer that creates microscopic grooves in the surface is rubbed on the side of the glass that does not have the polarizing film on it. The grooves must be in the same direction as the polarizing film. Then a coating of nematic liquid crystals is added to one of the filters. The grooves will cause the first layer of molecules to align with the filter's orientation. Then the second piece of glass is added with the polarizing film at a right angle to the first piece. Each successive layer of TN molecules will gradually twist until the uppermost layer is at a 90-degree angle to the bottom, matching the polarized glass filters.
As light strikes the first filter, it is polarized. The molecules in each layer then guide the light they receive to the next layer. As the light passes through the liquid crystal layers, the molecules also change the light's plane of vibration to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. If the final layer is matched up with the second polarized glass filter, then the light will pass through.
When an electric charge is applied to liquid crystal molecules, they untwist. When they straighten out, they change the angle of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no light can pass through that area of the LCD, which makes that area darker than the surrounding areas.
Because liquid crystal materials emit no light of their own, some LCDs come with built-in fluorescent tubes above, beside and sometimes behind the LCD. A white diffusion panel behind the LCD redirects and scatters the light evenly to ensure a uniform display. On its way through filters, liquid crystal layers and electrode layers, a lot of this light is lost - often more than half. With the availability of white colour LED, fluorescent tubes are beginning to be replaced by longer-lived LEDs.
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