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Prepared by:- BHADARKA DIVYA
About Liquid Crystal.
Liquid crystal molecules can move freely while maintaining their
It align itself to a polyimide film to the inside of a panel glass.
When the two glass panels are not aligned the liquid crystal twists
The liquid crystal will also align to electric field.
What is LCD?
LCD: Liquid Crystal Display is a thin, flat display device made
up of any number of thin crystals
The crystals act like tiny shutters, opening or closing in response
to the stimulus, thereby allowing degrees of light that have passed
through specific colored pixels to illuminate the screen, creating a
These display screens are used in televisions, computer monitors,
and cell phones
From CRT to LCD
 Bulky,
heavy, use vacuum tube
 Using
technology that was
developed in the 19th century.
 First
LCD laptop monitors were
very small due to manufacturing
 Light,
sleek, energy-efficient,
have sharp picture.
Liquid Crystal Display Principle
A liquid crystal display (LCD) is a thin, flat electronic
visual display that uses the light modulating properties
of liquid crystals (LCs). LCs do not emit light directly.
Liquid crystals are organic compounds, whose
macroscopic behaviour resemble that of liquid but
shows physical properties of crystals.
LCD TV uses twisted nematic liquid crystals.
Twisted Nematic type of display is most common
display and make use of twisted nematic phase crystals.
Twisted Nematic (TN) Display
Is the most common LCD Display.
The two alignments layer for the
liquid crystal material are orthogonal.
The light entering the polarize panel
rotates by the twist in the liquid
crystal and allowing it to pass through
the second polarize
Twisted Nematic (TN) Display
The electric field is applied
 Alight
to the electric field.
 Prevents
the rotation of the
polarized light
 The
liquid crystal loses its twist.
 The
second polarizer absorbs the
The applied voltage control the
absorbed and transmitted light
Twist Nematic Viewing Angle
Light passes through the TN display
from one angle may be blocked in
other angles by the twist of the
liquid crystal.
To overcome this limitation
different approaches have use
various orientations for the polarize
LCD (Liquid Crystal Display)
LCD Panel is based on
 A light
valve for each pixel that turn
the light on, off, or an intermediate
Grid of such light valve for the LCD
display panel.
A back light and display enhancement
films create the illumination.
Applying voltage to the
electrodes changes the level of
illumination in each sub-pixel
The panel is sandwiched
 Front
surface films to
enhance display property
 Backlight
Linear Polarized Light
Light usually vibrates in all
A linear polarized light limit the
vibration to one direction
It absorbs the component of
light that vibrate in all other
LCD require light to vibrate in
one direction.
Light Path
The light passes through the
 The voltage applied to the
electrodes controls the liquid
crystal orientation
 The liquid crystal orientation
controls the rotation of the
incoming polarized light.
 Color filters are used in color
LCD, where each color subpixel is controlled individually
The light generated by the backlight.
The light is evenly distributed the
light evenly over the LCD panel.
Display enhancement films are placed
between the light diffuser and the LCD
panel. They aim to maximize the light
reaching the observer.
Active Matrix Display
Allow very high resolution
Each sub-pixel is individually
controlled by an isolated thinfilm transistor (TFT).
It allows the electrical signal for
each sub-pixel to avoid
influencing adjacent elements.
The TFT is patterned into the
glass layer
A display with
1024x768 resolution
Include 1024x768x3
= 2,359,296 sub-pixels
Passive Matrix Display
Passive matrix display has
 Rows
of electrodes on one piece
of glass.
 Columns
of electrodes on the
opposing piece of glass.
 Complex
electrical waveform
control the voltage differential at
the intersection of the electrodes.
The intersection of the columns and
rows are the pixels
Advantages of LCD
Low power consumption
Slim profile and be wall mounted
Cost is low
Generally do not come in smaller size than 37 inches
More compact and light in weight
They have long life time
Achieves better and more accurate colour reproduction.
Disadvantages of LCD
Poor black level
Defective pixel problem occurs.
Slow response time than plasma.
Narrower viewing angles than competing technologies.
Computer monitors
They are common in devices such as video players,
gaming devices, clocks, wathces, calculators and