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Liquid Crystal Display (LCD)
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There's far more to building an LCD than simply creating a sheet of liquid crystals. The combination of four facts makes LCDs possible:
• Light can be polarized. Liquid crystals can transmit and change polarized light.
• The structure of liquid crystals can be changed by electric current.
• There are transparent substances that can conduct electricity.
An LCD is a device that uses these four facts in a surprising way!
To create an LCD, you take two pieces of polarized glass. 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. You then add a coating of nematic liquid crystals to one of the screen. The grooves will cause the first layer of molecules to align with the screen's orientation. Then add the second piece of glass with the polarizing film at a right angle to the first piece. |
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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 screen.
As light strikes the first screen, 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 screen, then
the light will pass through.
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If we apply an electric charge 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 screen. Consequently, no light can pass through that area of the LCD, which makes that area darker than the surrounding areas. An LCD that can show colors must have three subpixels with red, green and blue color screen to create each color pixel.
Through the careful control and variation of the voltage applied, the intensity of each subpixelcan range over 256 shades. Combining the subpixels produces a possible palette of 16.8 million colors (256 shades of red x 256 shades of green x 256 shades of blue). These color displays take an enormous number of transistors. For example, a typical laptop computer supports resolutions up to 1,024x768. If we multiply 1,024 columns by 768 rows by 3 subpixels, we get 2,359,296 transistors etched onto the glass! If there is a problem with any of these transistors, it creates a "bad pixel" on the display. Most active matrix displays have a few badpixels scattered across the screen. |
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Article ID: 2245 |
Last updated: 13 Oct, 2009 |
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Views: 3308
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Comments: 0
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