COMPUTER GRAPHICS & GAMING

LCD’S & LED’S…

- NOLESH PREMRAJ WARKE.

LCD’s

LIQUID CRYSTAL DISPLAY

> HISTORY…

-> LIQUID CRYSTAL DISPLAY WAS INVENTED BY

“GEORGE H. HEILMEIR” IN 1964.

-> LATER ON IMPROVEMENTS WERE DONE BY

“ JAMES FERGASON”

> What is Liquid Crystal Display…?

The LCD screen is based on the principle of blocking light rather than emitting it.

A LCD is a passive device which means it does not produce any light to display characters, images, video and animations.

It simply alters the light travelling through it.

LCD does not produce any illumination on its own it in fact depends on entirely on illumination falling on it from external source for its visual effect.

> Construction & Working…In single pixel area of LCD…

-> There are two polarization filters oriented at 90 degrees.

i) Vertically polarized filter.ii) Horizontally polarized filter.

-> Unpolarized light is passed through the first filter.

-> When the vertically polarized light passes through the second filter i.e horizontal filter no light output will get produced…

…..The vertically polarized light should rotate 90 degrees in order to pass through the horizontal polarized filter.

-> This can be achieved by embedding liquid crystal layer between both the filters.The liquid crystal layer consists of rod shaped tiny molecules.

The vertically polarized light passes through the liquid crystal layer and gets twisted to 90 degrees, when the orientation of light matches to the outer polarized filter the light will pass and brighten the screen.

-> If the liquid crystal molecules are twisted more precisely then more light will pass through it.

.....-> Two glass transparent ELECTRODES are aligned in front & back of liquid crystal in order to change the orientation of crystal molecules by applying voltage across it.

-> If there is no voltage applied across the electrodes then the orientation of molecules will remain twisted at 90 degrees and the light passes through the outer polarizer, thus the pixel appears white.

-> If the voltage applied is large enough then the liquid crystal layer changes its orientation (untwist) and then light will get blocked at the outer polarized filter , thus the pixel appears black(dark).

…..-> In order to produce color images a color filter is placed in front of the outer polarization plate.

Red, blue & green are the three standard color filters placed for every three pixels to produce different color images by varying the intensity of each color.

…..-> In this way, BLACK & WHITE characters or images are produced.

-> Generally the electrodes are made up of INDIUM TIN OXIDE (ITO) which is a transparent material so it is simply called as glass electrode plate.

-> LCD display is also called as “TWISTED NEMATIC LCD”.

> Types of LCD Displays-> Character LCD or Segment LCD Displays :-

The LCD displays will display all the alpha numeric values with some special characters including currencies symbols of different countries. These displays are not capable to produce any graphic animations or images.Used in : calculators, display panel, remote controllers.-> Graphical LCD Display :-

These LCD displays will display any monochrome graphical images and animations by energizing set of pixels in the LCD display. These are also capable to produce characters numbers and special symbols.

> Types of LCD Displays-> Color LCD Display :-

The LCD displays contains three sub pixels with primary colors Red, Blue & Green they can produce 16.77 million colors. These color displays require more number of transistors for its construction.Used in : Television, laptop screen, PC monitors.

> Advantages…

-> LCD’s consume less amount of power compared to LED and CRT.

-> LCD’s are thinner and lighter compared to CRT.

-> Does not get affected due to increase and decrease in air pressure

-> Includes millions of colors.

> Disadvantages…

-> Requires additional light source.

-> Limited range of temperature i.e o degree to 60 degrees.

-> Restricted viewing angle.

-> Speed is very slow.

Led’s

Light emitting diode

> LED’s…

-> An LED screen is actually an LCD screen, but instead of having a normal CCFL backlight ,it uses light emitting diode (led’s) as a source of light behind the screen .

An led energy is more efficient.

…..There are three main configurations of LED as backlights for televisionScreens :-

I ) Full array.II ) Egde lit.III) Direct lit.

….. full array :-

This method is considered the best LED backlight Type. The LED’s are distributed evenly behind the entire screen. This produces a more uniform backlight and provides a more effective use of local dimmimg.

….. Edge lit :-

This method is the most common method for LED TV’s. With an edge lit LED screen, the LED’s are placed at the peripheral of the screen. Depending on the television, it can be all around the screen or only on the sides or the bottom. This allows the screen to be very thin.Flashlighting or clouding.

….. Direct lit :-

This is how the lower-end LED TV’s are constructed.Similarly to the full array method the LED’s are directly behind the screen. These TV’s are not very thin because of the space required behind the screen to add the LED’sAnd to diffuse the light over a big area.

> Advantages…

-> Very long life.

-> Low maintenance.

-> High Efficiency.

-> Does not produce heat.

> Disadvantages…

-> LED’s are more expensive.

-> Limited range of temperature .i.e o degree to 60 degrees.

-> Restricted viewing angle.

-> Speed is very slow.

THANK YOU . . .