Lcd (Liquid Crystal Display)
Liquid crystal displays (LCDs) have emerged as a popular form of electronic display, particularly since the 1980s. They use very little electricity (a thousand times less energy than a LED (light-emitting diode) uses) and are easily visible, even in direct sunlight because they scatter light rather than produce it. In other words, they produce dark areas that may be seen in brightly illuminated environments instead of glowing lights that could be visually overpowered by brighter light sources. At the heart of a LCD is a material called a liquid crystal. First discovered in 1889, liquid crystals are fluid substances that have very well-ordered molecules, like those of solid crystals. When molecules of a material are aligned, they have a profound effect upon light passing through the material, often bending or splitting the individual light rays. In liquid crystals the molecules are parallel to one another and are arranged into planes, each one slightly offset from the last, creating a twisted pattern. As light passes through a liquid crystal, it is twisted and exits at a slightly different orientation from where it entered. In a LCD, a very thin layer of liquid crystal is sandwiched between two sections of glass. Each piece of glass is polarized so that it will only allow light of a certain direction to pass through. Normally, because the two glasses are not aligned, light passing through one section of glass would be blocked by the other; however, the sandwiched layer of liquid crystal twists the light enough to pass through the second section of glass.
Here, in the LCD's "off" position, the display is perfectly clear. To turn a LCD "on," an electrical charge must be applied to the liquid crystal. As the electrical field moves through the liquid, its molecules will line up with the direction of the field, "untwisting " the twisted planes. Light will now pass through the liquid crystal unaffected and be blocked by the second section of polarized glass. In this position the LCD appears black because it scatters all the light that enters. In order to show numbers, letters, or pictures on the LCD, tiny metallic segments must be baked onto the surface of the polarized glass. Each segment can be turned on or off independently, forming numbers and letters. While many calculators use a simple seven-segment display format, more complex devices, for example, such as hand-held video games and laptop computers, form whole screens, called dot-matrix screens, out of tiny LCD squares. LCD screens are being developed for desktop computers as well, offering the advantages of smaller footprint, less power consumption and flat screens. Some digital cameras utilized LCD displays for viewing images as well. While LCDs are used primarily for their legibility and low power consumption, they are essential in such dangerous industries as mining and chemistry. In these technologies LCDs are preferred for their very low voltage, current, and temperature-elements that, if too high, could start a fire or unwanted chemical reaction. Certain types of liquid crystals are also temperature sensitive and have been used in thermometers.
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