Monday, October 15, 2001		On Hardware

THE journey of monitors started with lumbering monochrome monitors and is still moving with a formidable technology of CRT monitors. For decades the bulky, square-shaped CRT (Cathode Ray Tube) monitors ruled the market because they provided quality and were economically cheap. But now the monitor industry has got a new lease of life. Here comes the new face of your computer — the elegant, slim and cool LCD or TFT monitors i.e. Liquid Crystal Display or Thin Film Transistors.

LCD is a digital display that uses liquid crystal cells that changes the reflectivity in an applied electric field, used for laptops, personal computer, calculators and digital watches.

In LCD monitors, the whole scene revolves around the liquid crystals. The origin of the liquid crystal research is generally credited to the Austrian Botanist Friedrich Reinitzer in 1888. This was an accidental discovery. At that time he was investigating the role of cholesterol in plants and experimenting with Cholesteryl Benzoate. This substance was solid at room temperature and when subjected to heat it changed its properties. However, the LCD technology was not able to capture the market because these liquid crystal were unstable and unsuitable for mass production. It was only when the British scientist discovered Biphenyl, a stable liquid crystal material, that made it possible for LCD technology to take off.

There are two different types of LCDs

a) DSTN — Dual-scan twisted nematic or Passive matrix display

b) TFT — Thin Film Transistor or Active matrix display

The oldest of the matrix technologies i.e. DTNS is now obsolete. It offers sharp text but leaves shadow images on the screen when the display changes rapidly. These days LCD monitors solely use TFT-based panel that can provide bright, sharp display in much larger sizes.

LCD is made of several layers that are arranged to the following order — Polarising filter, Sheet of glass, Electrode, Alignment layer, Liquid crystal.

The screen of the TFT LCD panel looks like a multi-layered sandwich that is made up of two perpendicular glass substrate. Between the substrates are the thin film transistors, colour filter panel that provides the necessary Red, Blue, Green primary colours, the liquid crystal layer and there is a fluorescent backlight that illuminates the screen from beneath.

When there is no electrical charge the liquid crystal remains amorphous. Liquid crystal changes its properties when subjected to varying amount of electrical charge. In this change, the liquid crystal allows different amount of light to pass through.

In LCD monitors the red, green, blue chamber are used that makes up one pixel. By subjecting the red, green, blue chambers to varying degrees of electrical charges, different colours can be achieved. The entire screen is made up of grid of pixels having a transistor turning it on or off. This is where a user gets the resolution.

1) LCDs are slim, elegant and compact, easy to fit on those table that are always cluttered with files and paper. In short, they requires less space.

2) LCDs have lower power requirement or voltage than CRTs, making them useful in battery-powered devices like laptops or palmtops.

3) CRTs emit small amounts of radiations, i.e. electromagnetic radiations but LCDs don’t emits these radiations.

4) The big problem of CRTs is flickering which is not the case in LCD monitors.

5) LCD monitors provides full viewable size but this facility is not available in CRT monitors.

6) CRTs are able to display more resolutions than LCD monitors.

7) CRTs requires analogue and LCD monitors require digital signals.