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Overview of LCD Liquid Crystal Display

Updated: Mar 24

Introduction

LCD stands for Liquid Crystal Display in its entire form. LCD stands for liquid crystal display system, which is widely utilized on computer and television screens these days. These LCDs operate primarily on liquid crystals rather than cathode rays, which sets them apart from the earlier CRT displays.


As a passive device, it doesn't provide any light for the display of images, animations, movies, etc. While LED offers a clearer image than LCD, LCD employs fluorescent bulbs to brighten the image.

The LCD is made up of millions of crystal-created pixels arranged in a rectangle pattern on the LCD. Every pixel on an LCD is illuminated by backlights. Each pixel has an RGB sub-pixel—red, green, and blue—that may be turned on or off. It appears black when every subpixel is turned off and white when every subpixel is turned on 100% of the time.


What is Liquid Crystal

According to certain theories, liquid crystals represent the fourth state of matter. They are neither solids nor liquids, which explains why. However, they have the characteristics of a crystal and the capacity to flow or move like liquid. The molecular orientation of their crystalline structure is similar to that of a solid. These molecules do, nonetheless, also exhibit mobility in different orientations. Hence, it possesses both solid and liquid properties. Consequently, liquid crystal is referred to.


Construction of LCD-Liquid Crystal Display

The pictures or characters are shown by this liquid crystal when the light from the source is either passed through or blocked by the crystal's molecular mobility. Generally, twisted- nematic-type crystals are employed in liquid crystal displays. This is because the twisted- nematic crystal's molecules have a slight natural twist that is about 90° in angle. The molecules exhibit varying degrees of untwisting in accordance with the applied voltage.


The liquid crystal is sandwiched between two sheets of glass, with a thickness of around 10 to 20 micrometers. Conductors are put on the inner surface of the two glass sheets. These wires combine to create electrodes. Positive and negative polarities are indicated for application on the two electrodes. These two electrodes provide the display unit with the external potential. Basically, materials like stannic oxide (SnO3) and indium oxide (IN2O3) generate these.


The light source employed here is fluorescent. The polarizer receives the light emitted by this source, after which it is fed; in this case, a vertical polarizer is used as the input polarizer. Furthermore, at the other end of the display unit is a polarizer with the opposite polarity as the input. The polarizer at the other end must thus be horizontal if we are assuming that this is a vertical polarizer as the input polarizer. There is a glass cover that displays the desired picture at the other end of the electrode.


LCD is a mixture of two different states of matter: liquid and solid. The visible picture is made up of the liquid and the solid component, which is crystal. Two polarized panels, filters, and electrodes make up the two layers that make up an LCD. Instead of generating light, LCD screens function by obstructing it. LCD pixel grids come in two varieties:


Active Matrix Grid: This technology is more recent. This technique is used on smartphones that have LCDs.

Passive Matrix Grid: This technology is more ancient. This technique was utilized in certain older gadgets.


Working of LCD-Liquid Crystal Display

LCDs are not electroluminescence devices, as we already know. This indicates that it uses a liquid crystal to transform light into a bright or dark appearance, rather than possessing the ability to produce light. Let's go forward and see how an LCD works now.


The following figure will assist you in better comprehending how an LCD functions:


When the vertical polarizer is exposed to light coming from a backlight source. After that, the source's unpolarized light becomes vertically polarized. Initially, in the absence of any external voltage between the two electrodes, the liquid crystal molecules stay twisted. Because of the molecules' orientation, this results in the vertically polarized light being horizontally polarized.


As we've mentioned, the two polarizers are 90 degrees aligned with one another. As a result, the polarizer situated at the other end is horizontal in nature. As a result, the pixel is illuminated when the horizontally polarized light from the nematic crystal's output is passed into the horizontal polarizer. Produces a picture that is displayed on the screen as a result.


Imagine that there is a high voltage placed between the two electrodes. The molecule's twisted mechanism is then harmed by the supplied voltage, which makes them behave straight. As a result, the vertically polarized light does not alter in polarization when it passes through the nematic crystal. This results in a black pixel at the display by preventing the vertically polarized light from passing through the horizontal polarizer. Images that are both brilliant and black are produced in this manner.



Characteristics of LCD-Liquid Crystal Display

Resolution:

Light enters the liquid crystal, which makes up LCDs, and reflects light in a well-formed manner. A liquid crystal is neither liquid nor solid. Thus, the image created by this liquid crystal is incredibly precise. An LCD is a digital display that uses a fixed matrix of vertical and horizontal dots to address each individual pixel. The LCD adjusts the image's scaling based on the device's resolution. Thus, there is no loss of visual quality.


Brightness:

Brightness is measured in nits and refers to the light that the LCD emits, which is just visible light intensity. One candela per square meter is known as a nit. For decent resolutions and pixel counts, LCD brightness is highly accurate.


Contrast Ratio:

It is the ratio that the display provides between the brightest and darkest color at a specific location on the screen. See the formula below to compute the contrast ratio (CR):


Contrast Ratio

Response Rate:

LCDs have higher response rates than CRTs because it takes significantly less time for pixels to change color. This results in higher refresh rates on LCDs. A pixel's transition from one image to another is seamless.



Types of LCD-Liquid Crystal Display


Twisted-Nematic (TN)

Which are cheap but have fast response times. Conversely, poor contrast ratios, viewing angles, and color contrasts are characteristics of TN screens. Because TN LCDs are used in so many different kinds of displays across sectors, they are manufactured widely.


Panel Switching displays (IPS Panels)

In-panel Switching displays (IPS Panels) feature far greater contrast ratios, viewing angles, and color contrast than TN LCD's. In Panel Switching displays provide better contrast, brighter color accuracy, and image quality than TN LCD's.


Vertical Alignment Panels (VA Panels)

In between TN and IPS screens, Vertical Alignment Panels (VA Panels) are thought to be intermediate. Between twisted nematic technology and in-plane switching panels, vertical alignment panels are seen to provide a decent middle ground. In contrast to TN-type displays, this kind of panel offers the greatest viewing angles and higher-quality color reproduction.


Advanced Fringe Field Switching (AFFS)

Better than most IPS displays in terms of color reproduction. With several possibilities for color reproduction, the AFFS LCD is a high-performing display. These displays generate images of excellent quality. In high-tech applications such as functional airplane cockpits, these displays are most frequently utilized.


Advantages of LCD


  • In comparison to CRT and LED displays, less heat is produced during operation.

  • Compared to other display devices, an LCD consumes a very small amount of power.

  • MOS-integrated circuits can be used appropriately with LCDs.

  • The device has a low total cost.


Applications of LCD


  • A television, calculator, computer monitor, and other electronic devices screens are among the many places LCD is used to display images.

  • These are also utilized on mobile screens and smartwatches.

  • In addition, they are employed in medical applications such as liquid crystal thermometers and in waveguides for the visualization of radiofrequency waves.


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