The working principle and life of LCD

Oct 6, 2021 | Articles

The Working Principle and Life of LCD

Outline

1. Working Principles of LCD Display
2. LCD Voltage
3. Viewing Angles of LCD Display
4. Backlight of LCD Display
5. LCD Display Forms
6. Twisted Nematic (TN) LCDs Display
7. High Twisted Nematic (HTN) LCD display
8. Super Twisted Nematic (STN) LCD Display
9. Film Compensated Super Twisted Nematic (FSTN) LCD Display
10. VA LCD Display
11. Polarizers of LCD Display
Conclusion

 

Everything is changed under the sun because this is an era of science. As we compare past centuries to the present, we observe that much more new advancement in the field of science and technology. All these recent advancements make our life easier and better than in the past. Today’s cell phones, laptops, the internet, and many other technologies help us connect the world. Among all these inventions and discoveries, the most important innovation in science is the liquid crystal display (LCD), which changed our lives. The LCD is restricted to the display of a calculator. Still, now this latest technology can be seen in every home, office, hospital, and airport in the form of television, laptop computer screen, monitor, digital cameras, and many other digital devices.
In this article, we discuss the working principle of this amazing device and interesting facts about the life of LCD displays.

1. Working Principle of LCDs Display

The working of LCDs is to block light. Basically, it does not precede its own light because it uses an external light source. When the light source passes through the polarizer, an external supply is given to LC (liquid crystal). The polarized light aligns itself, and an image is created on the screen. To briefly discuss the working principle of LCD display, we introduce LCD fluid forms, basic modes, viewing angle, and polarizers of the monochrome display. All these modes are the basis of the working principle of the LCD screen.

2. LCD Voltage

LCD Voltage

Generally, the voltage of LCDs is from 2.8V to 5V. Normally, we suggest 3.0V or 3.3V. If you use a slightly lower voltage to drive the display, its font color will become a little darker; on the contrary, if you use a slightly higher voltage to drive the display, its font color will become darker.

3. Viewing Angles of LCD Displays

Viewing angles of LCD displays

Viewing angles should be discussed from actual applications. Generally speaking, the six o’clock direction and the twelve o’clock direction are terms in the industry. To put it simply, the six o’clock direction is to look from the bottom up, and the twelve o’clock direction is to look from the top down. Correspondingly, the 3 o’clock and 9 o’clock directions that we seldom use are looking from left to right and looking from right to left. Generally speaking, we use the 12 o’clock and 6 o’clock directions the most.
Generally speaking, the viewing angle direction is determined by the use characteristics of the terminal product. For example, all kinds of meters and household equipment are all at 6 o’clock. But it should be noted that the viewing angles at 6 o’clock and 12 o’clock will look very close. But if you look closely, you will find that the difference is the depth of the font color. For example, a display with a viewing angle of 6 o’clock is very clear when viewed from the 12 o’clock direction, but it will appear slightly dim compared to the 6 o’clock direction.
Therefore, the viewing angle of the display screen needs to be determined according to the application of the terminal product. We generally suggest the corresponding perspective based on the customer’s product.
In addition, some customers require a wide viewing angle. Here, because it involves the difference of display types, liquid crystals and polarizers and so on. Let’s briefly summarize it. The viewing angle size from narrow to wide is TN, HTN, STN, FSTN, DSTN. The reason why we don’t talk about VA here is that it is special. Because it is white on a black background, its viewing angle is theoretically super wide. But it is not easy to compare directly. So we will not discuss it for the time being, but it is worth noting that VA is generally used in car display devices.

4. Backlight of LCD Display

LCD Display Backlight

LCD display creates management of visible light. In the absence of this light, we add a backlight during making LCD displays for visibility. Many choices to obtain one of them are appearance vs. cost. The display modules are integrated with different types of the backlight. What we usually use for LCD displays are LED backlights. Because it’s easy to make custom designs and easy to control the brightness. And it has lots of color options. Normally, the backlight will be white. Orange and green, blue, red are also commonly used.
And if customers want to get high brightness, there are 2 ways to increase the brightness. First, increase led beads. Second, change the LED types(Use high brightness LED beads).

5. LCD Display Forms

LCD Display Forms

To describe liquid crystal display, we discussed here four types, including TN, HTN, STN, and FSTN mode, VA we will also discuss here. These all modes help us to describe the orientation of light passing through LCD structures differently.

6. Twisted Nematic (TN) LCDs Display

Twisted Nematic

TN means that the liquid crystal molecules are twisted 90 degrees. Generally speaking, it is divided into two display types. The positive display is black on a white background; the negative display is white on a black background.

7. High Twisted Nematic (HTN) LCD display

High Twisted Nematic

HTN means that the liquid crystal molecules are twisted by 100 to 180 degrees. Generally speaking, it is divided into two display types. The positive display is black on a white background; the negative display is white on a black background. Because its liquid crystal molecules have a larger twist angle, its viewing angle is wider than that of TN.

8. Super Twisted Nematic (STN) LCD Display

Super Twisted Nematic

STN is liquid crystal molecules twisted 180 to 270 degrees. Generally speaking, it is divided into two display types. The positive display is black text on a yellow-green background; the negative display is white text on a blue background. Because the twist angle of its liquid crystal molecules is larger than that of HTN, its viewing angle is wider than that of TN and HTN.

9. Film Compensated Super Twisted Nematic (FSTN) LCD Display

Film Compensated Super Twisted Nematic

The reason FSTN has a wider viewing angle is that it has a layer of the polarizer and a layer of compensation film. So under normal circumstances, it looks yellow-green or grayish. And because it has an extra layer of compensation film than the general TN, it has a wider viewing angle.

10. VA LCD Display

Passsive Matrix Vertical Alignment

VA is also called PMVA. PMVA stands for passive matrix vertical alignment. It refers to a technique in which molecules are oriented orthogonal (“vertical”) relative to the display surface. The resulting optical effect is a very dark background color with a very wide and symmetrical viewing angle. So its display effect is white text on a black background. Similar to the negative display mode of TN and HTN. But it has a wider perspective. Applied to high-end equipment.

11. Polarizers of LCD Display

Polarizers of LCD Display

Every type of LCDs has two types of polarizer, front and rear. The front is viewing, and the rear displays to infuse light. Polarizer displays have three types, including reflective, transmissive, and transflective. The explanations of these three modes are given below.

a. Reflective Mode

Reflective Mode

The polarizer of the reflective LCD screen cannot be used with the backlight because the bottom film does not transmit light, and the content on the screen can only be seen clearly when the external light source is illuminated.

b. Transmissive Mode

Transmissive Mode

The transmittance of the polarizer of the transmissive mode LCD screen is generally about 40%, so it has the best backlight effect and the highest brightness. Although it can be used without a backlight. But we generally don’t recommend this, because then you can see the PCB motherboard and components behind it.

c. Transflective Mode

Transflective Mode

The transmissivity of the polarizer of the transflective LCD screen is generally about 30%, so it can be used without backlight or with backlight. Generally, high-end equipment with backlight switch control will use this type of display.

Conclusion

Applied in some products

The working principle of monochrome LCDs displays concluded that the best screen with viewing range, different color factor, and high availability. The LCD display is the latest technology with major applications in the field of science and technology as well as in electronic devices. Its huge applications are used in the medical field for the purpose of health. So the LCD screens are the basic need of our life. I hope this article helps you to understand more about monochrome LCD displays.

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