LCD LED short information. Working of lcd and led. Difference between lcd and led . computer graphics subject. Cathode ray tube.

1. - NOLESH PREMRAJ WARKE.

3. -> LIQUID CRYSTAL DISPLAY WAS INVENTED BY
“GEORGE H. HEILMEIR” IN 1964.
-> LATER ON IMPROVEMENTS WERE DONE BY
“ JAMES FERGASON”

4. 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.

5. 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…

7. 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.

9. -> 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).

11. -> 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.

13. -> 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”.

14. 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.
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.

15. 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.

16. -> 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.

17. -> Requires additional light source.
-> Limited range of temperature i.e o degree to 60 degrees.
-> Restricted viewing angle.
-> Speed is very slow.

19. -> 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.

20. There are three main configurations of LED as backlights for television
Screens :-
I ) Full array.
II ) Egde lit.
III) Direct lit.

21.  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.

22.  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.

23.  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’s
And to diffuse the light over a big area.

24. -> Very long life.
-> Low maintenance.
-> High Efficiency.
-> Does not produce heat.

25. -> LED’s are more expensive.
-> Limited range of temperature .i.e o degree to 60 degrees.
-> Restricted viewing angle.
-> Speed is very slow.