Liquid Crystal Displays

You wake up in the morning, glance at your alarm clock, and get ready for school. You microwave your breakfast, grab your music player and dash out the door, checking your wristwatch as you go. Once at school, you pull out your calculator and get ready for the big math exam. Did you know you have used liquid crystal display (LCD) technology five times already? LCD is common display technology, used often because it is thin, lightweight, and energy efficient.

What is a liquid crystal? You know that liquids and crystals are two states of matter; but how is it possible to be both a liquid and a crystal? Recall that particles in a liquid can slide past each other in a container, while particles in a solid are packed together and cannot move separately. Liquid crystals are long molecules that keep their orientation—if they were oriented side-to-side in a thin layer on a glass plate, they would keep that side-to-side orientation. Because of their liquid property, the crystals can move around almost like a school of fish. Therefore, they share characteristics with both solids and liquids. This unique property makes them useful for a variety of electronic applications.

How do LCDs work? Consider a digital watch, for example. If you look closely at it, you can see the numbers, even when they are not darkened. These are the tracks that are engraved in the middle layer of a display "sandwich." Two plates of glass make up the outer portion of this sandwich. The inner portion of the sandwich, the tracks, contains liquid crystals that are in their natural, "relaxed" state. In the relaxed state, light passes through the plates of glass, and is reflected out.

Polarization Digital Watch
Digital watch displays are made possible through LCD technology. The inset photograph shows a polarized light micrograph of a LCD.

If an electric current is applied across a track of liquid crystals, the crystals lose their original orientation. As long as a small current passes through them, light entering the plates of glass will not be reflected. In other words, that track will appear black.

Seems simple enough, right? That is why LCD displays are becoming more and more popular. They can be all black or color. There are, however, some flaws with LCD technology that need to be corrected. For example, it has a narrow viewing angle; if you tilt your watch slightly you can no longer see the numbers as clearly, if at all. With further research, however, LCD might just become the vision of the future.

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Earth Science

Diagram Visit glencoe.com to research the different layers of an LCD. Create a drawing showing all the different layers and how they fit together.

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Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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