How screen display works

Displays, often called monitors or screens, are the most-used output device on a computer. They provide instant feedback by showing you text and graphic images as you work or play.

Most desktop displays use Liquid Crystal Display (LCD) or Cathode Ray Tube (CRT) technology, while nearly all portable computing devices, such as laptops, incorporate LCDs. Because of their slimmer design and lower energy consumption, LCD monitors (also called flat panel or flat screen displays) are replacing CRTs.

Basic feature

Resolution refers to the number of dots of colour, known as pixels (picture elements), contained in a display. It is expressed by identifying the number of pixels on the horizontal and vertical axes. A typical resolution is 1024 x 768.

Two measurements describe the size of your display: the aspect ratio and the screen size. Historically, computer displays, like most televisions, have had an aspect ratio of 4: 3 – the width of the screen to the height is four to three. For widescreen LCD displays, the aspect ratio is 16: 9, very useful for viewing DVD movies, playing games and displaying multiple windows side by side. High- definition TV also uses this format. The viewable screen size is measured diagonally, so a 19” screen measures 19” from the top to the bottom right.

Inside the computer there is a video adapter, or graphics card, which process images and sends signals to the monitor. CRT monitors use a VGA (video graphics adapter) cable, which converts digital signals into analogue signals. LCD monitors use a DVI (digital video interface) connection.

Colour depth refers to the number of colours a monitor can display. This depends on the number of bits used to describe the colour of a single pixel. For example, an old VGA monitor with an 8-bit depth can generate 256 colours and a SuperVGA with a 24-bit depth can generate 16.7 million colors. Monitors with a 32-bit depth are used in digital video, animation and video games to get certain effects.

Display technologies

An LCD is made of two glass plates with a liquid crystal material between them. The crystals block the light in different quantities to create the image. Active-matrix LCDs use TFT (thin film transistor) technology, in which each pixel has its own switch. The amount of light the LCD monitor produces is called brightness or luminance, measured in cd/m² (candela per square metre).

A CRT monitor is similar to a traditional TV set. It contains millions of tiny red, green and blue phosphor dots that glow when struck by an electron beam that travels across the screen and create a visible image.

PCs can be connected to video projectors, which project the image onto a large screen. They are used for presentations and home theatre applications.

In a plasma screen, images are created by a plasma discharge which contains noble (non-harmful) gases. Plasma TVs allow for larger screens and wide viewing angles, making them ideal for movies.

Organic Light-Emitting Diodes (OLEDs) are thin-film LED displays that don’t require a backlight to function. The material emits light when stimulated by an electrical current, which is known as electroluminescence. They consume less energy, produce brighter colours and are flexible 0 i.e. they can be bent and rolled up when they’re not being used.

IV. Listen to five customers in a computer shop describing device needs. Which device (a-e) would you recommend to each person? In pairs, discuss your choice and give reasons for them.