What is an LCD Display : Construction & Its Working

At present, we look liquid crystal displays (LCDs) everywhere; however, they didn’t develop immediately. It took so much time to develop from the development of the liquid crystal to a large number of LCD applications. In the year 1888, the first Liquid crystals were invented by Friedrich Reinitzer (Austrian botanist). When he dissolved a material like a cholesteryl benzoate, then he observed that it initially it turns into a cloudy fluid & cleared up as its temperature rose. Once it is cooled, then the fluid became blue before lastly crystallizing. So, the first experimental liquid crystal display was developed by the RCA Corporation in the year1968. After that, the manufacturers of LCD have gradually designed ingenious differences &developments on the technology by taking this display device into an incredible range. So finally, the developments in the LCD have been increased.

What is an LCD (Liquid Crystal Display)?

A liquid crystal display or LCD draws its definition from its name itself. It is a combination of two states of matter, the solid and the liquid. LCD uses a liquid crystal to produce a visible image. Liquid crystal displays are super-thin technology display screens that are generally used in laptop computer screens, TVs, cell phones, and portable video games. LCD’s technologies allow displays to be much thinner when compared to a cathode ray tube (CRT) technology.


Liquid crystal display is composed of several layers which include two polarized panel filters and electrodes. LCD technology is used for displaying the image in a notebook or some other electronic devices like mini computers. Light is projected from a lens on a layer of liquid crystal. This combination of colored light with the grayscale image of the crystal (formed as electric current flows through the crystal) forms the colored image. This image is then displayed on the screen.

An LCD
An LCD

An LCD is either made up of an active matrix display grid or a passive display grid. Most of the Smartphone’s with LCD technology uses active matrix display, but some of the older displays still make use of the passive display grid designs. Most of the electronic devices mainly depend on liquid crystal display technology for their display. The liquid has a unique advantage of having low power consumption than the LED or cathode ray tube.

The liquid crystal display screen works on the principle of blocking light rather than emitting light. LCDs require a backlight as they do not emit light them. We always use devices which are made up of LCD’s displays which are replacing the use of cathode ray tube.  Cathode ray tube draws more power compared to LCDs and is also heavier and bigger.

How LCDs are Constructed?

Simple facts that should be considered while making an LCD:

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  1. The basic structure of the LCD should be controlled by changing the applied current.
  2. We must use polarized light.
  3. The liquid crystal should able be to control both of the operations to transmit or can also able to change the polarized light.
LCD Construction
LCD Construction

As mentioned above that we need to take two polarized glass pieces filter in the making of the liquid crystal. The glass which does not have a polarized film on the surface of it must be rubbed with a special polymer that will create microscopic grooves on the surface of the polarized glass filter. The grooves must be in the same direction as the polarized film.

Now we have to add a coating of pneumatic liquid phase crystal on one of the polarizing filters of the polarized glass. The microscopic channel causes the first layer molecule to align with filter orientation. When the right angle appears at the first layer piece, we should add a second piece of glass with the polarized film. The first filter will be naturally polarized as the light strikes it at the starting stage.

Thus the light travels through each layer and guided to the next with the help of a molecule. The molecule tends to change its plane of vibration of the light to match its angle.  When the light reaches the far end of the liquid crystal substance, it vibrates at the same angle as that of the final layer of the molecule vibrates. The light is allowed to enter into the device only if the second layer of the polarized glass matches with the final layer of the molecule.

How LCDs Work?

The principle behind the LCDs is that when an electrical current is applied to the liquid crystal molecule, the molecule tends to untwist. This causes the angle of light which is passing through the molecule of the polarized glass and also causes a change in the angle of the top polarizing filter. As a result, a little light is allowed to pass the polarized glass through a particular area of the LCD.

Thus that particular area will become dark compared to others. The LCD works on the principle of blocking light. While constructing the LCDs, a reflected mirror is arranged at the back. An electrode plane is made of indium-tin-oxide which is kept on top and a polarized glass with a polarizing film is also added on the bottom of the device. The complete region of the LCD has to be enclosed by a common electrode and above it should be the liquid crystal matter.

Next comes the second piece of glass with an electrode in the form of the rectangle on the bottom and, on top, another polarizing film. It must be considered that both the pieces are kept at the right angles. When there is no current, the light passes through the front of the LCD it will be reflected by the mirror and bounced back. As the electrode is connected to a battery the current from it will cause the liquid crystals between the common-plane electrode and the electrode shaped like a rectangle to untwist. Thus the light is blocked from passing through. That particular rectangular area appears blank.

How LCD utilizes Liquid Crystals & Polarized Light?

An LCD TV monitor utilizes the sunglasses concept to operate its colored pixels. On the flip side of the LCD screen, there is a huge bright light that shines out in the direction of the observer.  On the front side of the display, it includes the millions of pixels, where each pixel can be made up of smaller regions known as sub-pixels. These are colored with different colors like green, blue, and red. Each pixel in the display includes a polarizing glass filter at the backside and the front side includes at 90 degrees, so the pixel looks dark normally.

A small twisted nematic liquid crystal is there among the two filters which control electronically. Once it is turned OFF, then it turns the light to pass through 90 degrees, efficiently letting light to supply throughout the two polarizing filters so that pixel seems bright. Once it is activated then it doesn’t turn the light because it is blocked through the polarizer & the pixel seems dark. Every pixel can be controlled through a separate transistor by turning ON and OFF several times every second.

How to Choose an LCD?

Generally, every consumer doesn’t have much information regarding the different kinds of LCDs available in the market. So before selecting an LCD, they collect all the data like features, price, company, quality, specifications, service, customer reviews, etc. The truth is that promoters tend to get the benefit from the truth that most of the customers conduct extremely minimum research before purchasing any product.

In an LCD, motion blur can be an effect of how long a picture takes to switch and display on the screen. However, both of these incidents change very much among an individual LCD panel in spite of primary LCD tech. Selecting an LCD based on underlying technology must be more regarding price vs. preferred difference, viewing angles & reproduction of color than estimated blur otherwise other gaming qualities. The highest refresh rate, as well as response time, must be planned in any specifications of the panel. Another gaming tech like strobe will turn ON/OFF the backlight rapidly to decrease resolution.

Different Types of LCD

The different types of LCDs are discussed below.

Twisted Nematic Display

The TN (Twisted Nematic) LCDs production can be done most frequently and used different kinds of displays all over the industries. These displays most frequently used by gamers as they are cheap & have quick response time as compared with other displays. The main disadvantage of these displays is that they have low quality as well as partial contrast ratios, viewing angles & reproduction of color. But, these devices are sufficient for daily operations.

These displays allow quick response times as well as quick refresh rates. So, these are the only gaming displays which are available with 240 hertz (Hz). These displays have poor contrast & color because of the not accurate otherwise precise twist device.

In-Plane Switching Display

IPS displays are considered to be the best LCD because they provide good image quality, higher viewing angles, vibrant color precision & difference. These displays are mostly used by graphic designers & in some other applications, LCDs need the maximum potential standards for the reproduction of image & color.

Vertical Alignment Panel

The vertical alignment (VA) panels drop anywhere in the center among Twisted Nematic and in-plane switching panel technology. These panels have the best viewing angles as well as color reproduction with higher quality features as compared with TN type displays. These panels have a low response time. But, these are much more reasonable and appropriate for daily use.

The structure of this panel generates deeper blacks as well as better colors as compared with the twisted nematic display. And several crystal alignments can permit for better viewing angles as compared with TN type displays. These displays arrive with a tradeoff because they are expensive as compared with other displays. And also they have slow response times & low refresh rates.

Advanced Fringe Field Switching (AFFS)

AFFS LCDs offer the best performance & a wide range of color reproduction as compared with IPS displays. The applications of AFFS are very advanced because they can reduce the distortion of color without compromising on the broad viewing angle. Usually, this display is used in highly advanced as well as professional surroundings like in the viable airplane cockpits.

Passive and Active Matrix Displays

The Passive-matrix type LCDs works with a simple grid so that charge can be supplied to a specific pixel on the LCD. The grid can be designed with a quiet process and it starts through two substrates which are known as glass layers. One glass layer gives columns whereas the other one gives rows that are designed by using a clear conductive material like indium-tin-oxide.

In this display, the rows otherwise columns are linked to ICs to control whenever the charge is transmitted in the direction of a particular row or column. The material of the liquid crystal is placed in between the two glass layers where on the external side of the substrate, a polarizing film can be added. The IC transmits a charge down the exact column of a single substrate & the ground can be switched ON to the exact row of the other so that a pixel can be activated.

The passive-matrix system has major drawbacks particularly response time is slow & inaccurate voltage control. The response time of the display mainly refers to the capability of the display to refresh the displayed image. In this type of display, the simplest way to check the slow response time is to shift the mouse pointer fast from one face of the display to the other.

Active-matrix type LCDs mainly depends on TFT (thin-film transistors). These transistors are small switching transistors as well as capacitors which are placed within a matrix over a glass substrate. When the proper row is activated then a charge can be transmitted down the exact column so that a specific pixel can be addressed, because all of the additional rows that the column intersects are switched OFF, simply the capacitor next to the designated pixel gets a charge.

The capacitor holds the supply until the subsequent refresh cycle & if we cautiously manage the sum of voltage given to a crystal, then we can untwist simply to permit some light through. At present, most of the panels offer brightness with 256 levels for each pixel.

How Colored Pixels Works in LCDs?

At the backside of the TV, a bright light is connected whereas on the front side, there are many colored squares that will be turned ON/OFF. Here, we are going to discuss how every colored pixel is turned ON/OFF:

How the Pixels of LCD Switched OFF

  • In the LCD, the light travels from the backside to the front side
  • A horizontal polarizing filter ahead of the light will block all the light signals apart from those horizontally vibrate. The pixel of the display can be switched off by a transistor by allowing the flow of current throughout its liquid crystals which makes the crystals sort out & the light supplies through them will not change.
  • Light signals come out from the liquid crystals to vibrate horizontally.
  • A vertical type polarizing filter ahead of the liquid crystals will block all light signals apart from those signals vertically vibrating. The light which is vibrating horizontally will travel throughout the liquid crystals so they cannot get during the vertical filter.
  • At this position, light cannot reach the LCD screen because the pixel is dim.

How the Pixels of LCD Switched ON

  • The bright light at the backside of the display shines like before.
  • The horizontal polarizing filter ahead of the light will block all light signals apart from those vibrating horizontally.
  • A transistor activates the pixel by turning off the flow of electricity in the liquid crystals so that crystals can rotate. These crystals turn light signals by 90° as they move through.
  • Light signals that flow into the horizontally vibrating liquid crystals will come out from them to vibrate vertically.
  • The vertical polarizing filter ahead of the liquid crystals will block all light signals apart from those vertically vibrating. The light which is vertically vibrating will come out from the liquid crystals can now acquire throughout the vertical filter.
  • Once the pixel is activated then it gives color to the pixel.

Difference between Plasma & LCD

Both the displays like plasma and an LCD are similar, however, it works in a different way totally. Every pixel is a microscopic fluorescent lamp that glows through the plasma, whereas plasma is an extremely hot type of gas where the atoms are blown separately to make electrons (negatively charged) & ions (positively charged). These atoms flow very freely and generate a glow of light once they crash. The designing of the plasma screen can be done very bigger as compared with ordinary CRO (cathode-ray tube) TVs, but they are very expensive.

Advantages

The advantages of liquid crystal display include the following.

  • LCD’s consumes less amount of power compared to CRT and LED
  • LCD’s are consist of some microwatts for display in comparison to some mill watts for LED’s
  • LCDs are of low cost
  • Provides excellent contrast
  • LCD’s are thinner and lighter when compared to cathode-ray tube and LED

Disadvantages

The disadvantages of liquid crystal display include the following.

  • Require additional light sources
  • Range of temperature is limited for operation
  • Low reliability
  • Speed is very low
  • LCD’s need an AC drive

Applications 

The applications of liquid crystal display include the following.

Liquid crystal technology has major applications in the field of science and engineering as well on electronic devices.

  • Liquid crystal thermometer
  • Optical imaging
  • The liquid crystal display technology is also applicable in the visualization of the radio frequency waves in the waveguide
  • Used in the medical applications

Few LCD Based Displays

Few LCD based displays

Thus, this is all about an overview of LCD and the structure of this from the backside to the front side can be done using backlights, sheet1, liquid crystals, sheet2 with color filters & screen. The standard liquid crystal displays use the backlights like CRFL (cold cathode fluorescent lamps). These lights are consistently arranged backside of the display to deliver reliable lighting across the panel. So the brightness level of all the pixels in the picture will have equal brightness.

I hope you have got a good knowledge of liquid crystal display. Here I leave a task for you. How is an LCD interfaced to a microcontroller? furthermore, any queries on this concept or electrical and electronic project Leave your answer in the comment section below.

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10 Comments

  1. Raushan Kumar says:

    I am looking for a good article on How LCD work ? and this article help me lot for my blog.
    Thanks To Tarun

    1. Tarun Agarwal says:

      Hi Raushan
      Thank you for your positive comments

  2. C.GOVINDAN says:

    Working principles describe by block diagrams, by easy understanding of LCD tv , good articles

  3. Thank you for this information

  4. MADUABUCHI says:

    IT IS AN EDUCATIVE ARTICLE

  5. Maniruzzaman Akash says:

    Searching more for construction and working, and finally got. Not found in wiki also. Thanks admin.

  6. jay prakash rajpoot says:

    ok thank sir

  7. thank u for ur information

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