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[Science] Basic working principle of LCD screen

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Author : Mili-KTBABA
Update time : 2021-08-18 11:11:23
The purpose of writing such an article is disenchantment. "Disenchantment" is a philosophical word.  The dissolution of the mystery, sanctity, and charm of science and knowledge are the ones that I want to express. Today's marketing sanctifies technical terms, and the work of researchers is tainted by hype. In my opinion, it is important to understand the principles, advantages, and disadvantages of new technologies, and then say "That's interesting." Instead of "Awesome! Dumbfounded! Surprised! Boiling! Subversion!
 
So I want to use plain language to analyze some of the hotter technologies and concepts on the Internet. To put it bluntly, I want to resist bad smell marketing. As I am just a half-bottle water lover, this is difficult. But most of the things are based on current information, but the stench of marketing is pervasive and deeply rooted in the hearts of the people. There will inevitably be errors in the current learning and selling at current, and criticisms and corrections are welcome.
 
Three primary colors, pixels, sub-pixels
 
In the quality education stage, we learned the knowledge of the three primary colors, and then we took a look at how to display various colors on the screen.

 
The concept of screen pixel (pixel) should not need to be explained. A pixel is a display point, and several pixels in the horizontal and vertical directions are arranged to form a screen. When different pixels present different colors, an image appears on the entire screen.
 
But how does a specific pixel display different colors? Of course, it is still a mixture of RGB's three primary colors. A pixel contains three tiny color blocks of red, green, and blue, and this color block can be called a sub-pixel.
 

 
 
Each of the three sub-pixels participates in different amounts of the LCD screen, and the colors presented by the pixels are different. How to adjust the amount of participation of sub-pixels during display? Now we officially begin to understand the principle of an LCD screen display.
 
How does the LCD screen work?
 
The LCD screen needs a backlight, which is white light, and the white light penetrates the colored film to display colors.

 
But the screen display content will change, that is, the backlight needs to be adjusted, which is achieved through the liquid-crystal layer. Before that, we first add two polarizers to the screen, one vertical and one horizontal. When the backlight passes through the first polarizer, only part of the light corresponding to the polarization direction of the polarizer can pass, but because the direction is perpendicular to the second polarizer, it cannot pass through, and the screen is black.

 
Then use the liquid crystal to adjust the direction of the polarized light after the first polarizer, as a result, it can pass through the second polarizer.
 
About the liquid crystal, it has unique optical properties. The light can go along the crystal with the direction for the diffuse, the liquid crystal will distort the direction of polarized light. With the correct operation, the polarized light after passing through the first polarizer can be rotated to make it pass through the second polarizer.

 
But what is showed on the screen at this time is still white, how to adjust it to other colors? Liquid crystals also have a unique electromagnetic property. Liquid crystal molecules in an electrostatic field will induce induced charges and generate electrostatic torsion, which changes the arrangement of the liquid crystal molecules. The permutation direction of the liquid crystal molecules is changed by the electrostatic field, and the direction of rotation of the passing light naturally changes. Therefore, it is also necessary to add a pair of electrode plates on both sides of the liquid crystal layer, and adjust the voltage between the electrode plates to control the degree of distortion of the liquid crystal molecule arrangement, thereby controlling the amount of light passing through the second polarizer, and finally showing a variety of Kind of color.

 
Well, the above is the general working principle of the LCD screen. Here is a more detailed diagram copied from Wikipedia.

 
Thanks for your time to read it,and I hope you can come to discuss with me.I will share more in the following days as well.
 
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