LCD SCREENS SPH4U By Gazoan Ahmed

Introduction Physics is applied in everyday life; LCD screens are one of the most used technology in today’s modern society. They are found in our cellphones, TVs, cars, computers, etc. In this presentation, the function and rule of each component in LCD screens will be explained!

Components of the display and their function To understand the way LCDs work, it is helpful to understand the function of each component. The polarization filter is a grid made up of many gridlines close together that allow light waves in one direction to go through. The polarized light then passes onto the liquid crystals.

Function continues LCD’s consist of a bright white light source behind the polarizing filter. In front of the polarizing filter, there are many liquid crystal molecules. There is another polarization filter that is placed on the other side of the liquid crystals whose gridlines are at 90° to the other polarizing filter. In front of the second polarization filter, are millions of pixels (individual picture element). Each pixel is made up of 3 sub-pixels colored red, green, and blue.

Liquid crystals Liquid crystal (LC) is a state of matter, just like solid, liquid, and gaseous states. Similar to their name, liquid crystals have properties that are between solids and liquids. There are many sub-states (phases) for LC. However the LC that is used in LCD is the twisted nematic phase (properties are closer to liquid in this phase). LCs are affected by electrical current. When an electrical current is applied to the twisted nematic LC, it will untwist, prohibiting the polarized light to go through the other polarizing filter. In essence, a pixel in the LCD is controlled by its own transistor, which blocks electrical flow to the liquid crystals to keep them twisted, letting the light to shine through (shown in the diagram below). To summarize, LCD does not emit light it simply allows or blocks it.

Diagram

Affects on people and society Advantages: Energy efficient. Consume less than 1/3 the power of a comparable CRT. Consume less electricity than a CRT and produce little heat. Take up about 40% less desk space. LCDs are thin and compact. Disadvantages: LCD screens became part of our daily life. Using them in cellphones, TV's and computers will have an impact on our vision on the long run LCD screens need to be disposed in safe way, like batteries and other harmful martials. Wrong disposal will harm the environment!