Further information on Monitors

Screen sizes are measured diagonally and are still quoted in inches. Popular sizes are 15 inches (38 cm) and 17 inches (43 cm). Larger monitors make working at a computer easier on the eyes and are essential for use in DTP (desktop publishing) and CAD work. 

Cathode ray tubes (CRTs):

• CRT monitors are similar in many ways to a television. They use cathode ray tubes (CRTs) containing an electron gun at the back of the tube which fires electrons at groups of phosphor dots coating the inside of the screen. When the electrons strike the phosphor dots they glow to give the colours.  On a colour monitor each group of phosphor dots is made up of one green, one blue and one red dot (RGB). By varying the brightness of each of these primary colours, the whole group will appear to the human eye as any colour possible. One group of dots is called a pixel (short for picture element).
• Because you sit very close to a computer monitor and need to be able to read small text, the pixels need to be very close together. The spacing of the pixels determines the clarity, or resolution, of the screen image. A typical distance between the pixels on a computer monitor is 0.28 mm.  Three standards currently in use are:
  • VGA (Video Graphics Array) 640 x 480 pixels
  • SVGA (Super Video Graphics Array) 800 x 600 pixels
  • XGA (Extended Graphics Array) 1024 x 768 pixels.

How the 3 coloured dots (RGB) in a screen pixel can combine:
Black screen	This diagram shows how phosphor dots of the 3 primary colours RED, GREEN and BLUE (RGB) can be ADDED together to form the three secondary colours and white. The diagram shows what happens when each dot has an equal brightness, varying the brightness of each of the dots produces all the other possible colours. R + B = magenta B + G = cyan G + R = yellow R + G + B = white

Other displays: 

• Liquid crystal displays (LCDs) - these use tiny crystals which, when a charge is applied across them, polarise the light passing through them. Used in combination with special filters, this means that light will not pass through when an electrical charge is applied. LCDs are also used in watches and calculators. They use much less power than a normal monitor and are also used in watches and calculators.
• Thin film transistors (TFTs)  - this is a more advanced type of display, giving full colour and high quality output. Each pixel on the screen is controlled by its own transistor and this provides a higher resolution and more contrast.