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Working Principle

Understanding the basic working principle of the digital display technologies will help understand the following sections more easily. A digital image is produced by a rectangular array of picture elements (pels or pixels). Each pixel in the display panel is made of three sub-pixels for the three additive primary colours: red, green and blue. All shades of colours from bright white to pitch black are produced from the mixture of these colours. (Image from http://www.tomshardware.com/2005/03/09/lcd_or_plasma_/index.html)



'Digital Image Components' 

Fig 1: Digital Image Components

Plasma display consists of two transparent glass panels sandwiching a thin layer of pixels. Each pixel is made of three gas filled cells. The gas used is a mixture of inert gases neon and xenon. A grid of tiny electrodes supplies electric current to these sub-pixels, as a result of which the gas ionizes to plasma state. Buyers need not worry about the leakage of this gas as they come in completely sealed units. This ionized gas emits high frequency UV rays, stimulating the cell’s phosphors to glow to the desired colour.

In a LCD display each pixel acts as a switch, they don’t emit any light. Instead there is a white back lighting. This light passes through the liquid crystal then through colour filter. The liquid crystal solution is trapped between two polarised glasses. Each sub-pixel is controlled electrically and thus more or less light is allowed to pass through the crystal, then through the polarised glass on to the display surface. Controlled red, green, and blue shades are thus emitted.

Digital Light Processing (DLP) TVs are the best technology for very large screens. Optical semiconductors are used. They are basically tiny mirrors that control the red, green, and blue sub-pixels on the screen. They don’t have the inherent burn-in disadvantage of Plasma technology or the lack of true blacks as in LCDs. The only disadvantage being they are not thin and you cannot hang on a wall.