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Liquid crystals are commonly used in electronic visual displays for a wide range of applications, and the consumer electronics market drives the development and innovation of these devices. It may seem unusual that a material that does not generate light would be of use as a display material, but the optical properties of liquid crystals as a modulator make it a very effective in this role. In addition, the liquid crystal device screen is more energy efficient than other display systems, making it an ideal choice for portable devices that rely on batteries to supply power.
The idea of modulating light through two polarizers is not new. When two polarizers are aligned, the light passes through, but when the polarizers are crossed or rotated 90 deg to each other, the light is blocked. With the polarizers in the crossed state, a thin sheet of clear plastic inserted between them will scramble the polarized light passing through, and the crossed polarizers will transmit light once again. This effect is at the core of the concept of using a liquid crystal material between crossed polarizers. The electrical switching capability can turn on and off the transmission of the liquid crystal, thus explaining the origins of liquid crystal use as a light modulator as well as clarifying how current displays evolved.
The rather simplistic idea of a liquid crystal light modulator quickly
evolved into a liquid crystal display (LCD) consisting of an electronically modulated optical system that can have any number of segments. Rather than relying on the liquid crystal material to scramble light, the material was used to guide the desired polarization of light between the polarizers. The early result from this approach is the standard seven-segment display, consisting of seven individually addressed segments. This is an example of a low-segment-count device that is commonly in use. Higher numbers of segments are required to produce an image, in which case the segments are referred to as pixels. Liquid crystal imaging displays can have many millions of pixels and are often square elements with a pixel pitch (the distance between the start of consecutive pixels) on the order of 200 mm. On typical displays, the number of pixels per inch ranges from 100 to more than 300.
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