25-02-2013, 03:11 PM
LIQUID CRYSTAL DIOD
LIQUID CRYSTAL.ppt (Size: 105.5 KB / Downloads: 22)
INTRODUCTION
A (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals
The LCD is more energy efficient and can be disposed of more safely than a CRT
LCDs are used in a wide range of applications including computer monitors, televisions, instrument panels,
HISTORY
In 1888, Friedrich Reinitzer (1858–1927) discovered the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and generation of colors) and published his findings at a meeting of the Vienna Chemical Society
In 1972, the first active-matrix liquid crystal display panel was produced in the United States by Westinghouse
The origins and the complex history of liquid crystal displays from the perspective of an insider during the early days were described by Joseph A. Castellano in Liquid Gold
OVERVIEW
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 (in most of the cases) perpendicular to each other
The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state
Displays for a small number of individual digits and/or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment. In
SPECIFICATION
Resolution versus range: Fundamentally resolution is the granularity (or number of levels) with which a performance feature of the display is divided
Spatial performance: LCDs come in only one size for a variety of applications and LCD spatial performance is also sometimedescribed in terms of a "dot pitch".
Color depth or color support is sometimes expressed in bits, either as the number of bits per sub-pixel or the number of bits per pixel.
Brightness and contrast ratio: Contrast ratio is the ratio of the brightness of a full-on pixel to a full-off pixel and, as such, would be directly tied to brightness if not
ENVIORMENT EFFECTS
The production of LCD screens uses nitrogen trifluoride (NF3) as an etching fluid during the production of the thin-film components. NF3 is a potent greenhouse gas, and its relatively long half-life may make it a potentially harmful contributor to global warming. A report in Geophysical Research Letters suggested that its effects were theoretically much greater than better-known sources of greenhouse gasses like carbon dioxide. As NF3 was not in widespread use at the time, it was not made part of the Kyoto Protocols and has been deemed "the missing greenhouse gas