Contrast ratio
A specification used for LCD screens, the contrast ratio is the difference in brightness between the brightest white and darkest black, and expressed as a ratio. A high contrast ratio is important to ensure a clear picture, especially with high contrast detail such as black text on a white background. Most modern LCD screens have a contrast ratio in excess of 400:1.
CRT (Cathode Ray Tube)
The venerable CRT is the basis of most televisions and computer monitors today, although it is being rapidly replaced by LCD technology. A CRT works by firing a stream of electrons from a cathode through a vacuum inside a tube at a screen that is coated in phosphors. These phosphors emit visible light momentarily when struck by the electron stream. A pair of anode coils then direct the stream vertically and horizontally across the screen many times per second to 'paint' the picture.
Dead pixel
A dead pixel can be defined in many ways by LCD screen manufacturers. Each pixel is actually made up of a red, green and blue sub-pixel, and some manufacturers will call it a dead pixel if any one of these is stuck on or off. Other manufacturers require an entire pixel (three sub-pixels) to be stuck. It is important to check your warranty conditions to see what level of protection you have from dead pixels.
DVI
A relatively new connector specifically designed for digital displays, such as LCDs and plasma screens, although the DVI-I standard can also carry an analogue signal. The digital-only format, DVI-D, can handle resolutions up to 1280 x 1024 at 85Hz or 1920 x 1080 at 60Hz.
Flat CRT
Flat CRT technology is similar to Trinitron in that it improves the image quality of CRTs. As the name implies, a flat CRT has a flat screen in one or both dimensions unlike a regular CRT, which is curved. Many flat CRTs use aperture grilles instead of shadow masks.
LCD (Liquid Crystal Display)
An LCD works by passing light from florescent tubes through two opposed polarised screens separated by a layer of liquid crystals. Given the two polarised screens are at 90 degrees to each other, they will normally not let light through. However, by applying a small electric current to the liquid crystals, they will twist, which will also twist the light passing through the crystal by 90 degrees. This means the light will then pass through the outer polarised screen to strike another layer of phosphors, much like in a CRT. By selectively switching individual liquid crystals on and off, the screen can display a full image. As each liquid crystal cluster corresponds to a single pixel, the picture is very crisp and clear at the screen's native resolution, although the screen is forced to interpolate other resolutions, resulting in blurring and reduced image quality.
Unlike CRTs, which 'draw' the screen from top left to bottom right row by row, an LCD can light all the phosphors simultaneously, meaning they don't suffer the same issues as CRTs such as flickering. LCDs are susceptible to other issues though, such as motion blur (see Response time), dead pixels, low contrast and poor viewing angles.
Plasma screen
A relatively new display technology that has individual cells containing a plasma gas that emits light when electrically stimulated. Plasma screens have many features in common with LCDs, such as a flat screen and crisp detail (due to each cell cluster corresponding to exactly one pixel), although plasma screens can be made significantly larger than LCDs. As such, plasma screens are usually used for outdoors and public display as well as televisions.
Response time
Usually measured in milliseconds, this is the time it takes for a pixel on an LCD screen to cycle from off, to on, then to off again. If the liquid crystal cannot switch fast enough it will result in a form of motion blurring on the screen. Most current LCD screens offer response times of 16ms, which makes the motion blur almost imperceptible. CRTs have a response time of around 1ms, which is the time it takes a phosphor to cycle from light to dark, so they still have the edge in applications with lots of motion, such as gaming.
TFT (Thin Film Transistor)
An advanced form of LCD screen that is used in the majority of flat panel displays for desktops and notebooks today. TFT technology allows very fine variations in brightness which allows a greater colour depth and greyscale to be displayed.
Trinitron
A technology developed by Sony to improve the quality of CRT displays. Normal CRTs have a 'shadow mask' on the inside of the screen with thousands of tiny holes that let the electron beam through to strike the phosphors. A Trinitron uses an aperture grille, which replaces the holes with rectangular 'slots'. This format means more light can pass through the grille, making the monitor brighter for the same power output. It also means the picture is sharper than most shadow mask CRTs. The final feature of Trinitrons is a flat screen in one dimension, while conventional shadow mask screens are curved in two dimensions.
VGA (Video Graphics Array)
A standard graphics format that originated with IBM PCs in 1987, but is now used across all modern PCs. VGA used a 15-pin connector, often referred to as D-Sub, and had a resolution of 640 x 480 with up to 16 colours from a palette of 262,144 colours. Since then VGA has been extended to include higher resolutions and colour depths. XGA, for example, features a 800 x 600 resolution with 16.8 million colours or 1024 x 768 at 65,536 colours. The resolutions above this are not uniform standards, but are commonly supported by most graphics cards and monitors.