What is the working principle of an lcd liquid crystal screen？

Hello everyone! Today, I'm going to analyze the working principle of lcd liquid crystal screens for you, so that you can have a better understanding and knowledge.

The physical properties of liquid crystals are as follows: when electrified, they conduct, and their arrangement becomes orderly, making it easier for light to pass through. When not powered, they are arranged in a disorderly manner, blocking light from passing through. Let the liquid crystal act like a gate to block or allow light to pass through. Technically speaking, a liquid crystal panel consists of two rather delicate sodium-free glass materials, known as Substrates, with a layer of liquid crystal in between. When the light beam passes through this layer of liquid crystal, the liquid crystal itself will stand in rows or twist into an irregular shape, thus blocking or allowing the light beam to pass through smoothly. Most liquid crystals are organic complexes composed of long rod-shaped molecules. In their natural state, the long axes of these rod-shaped molecules are roughly parallel. When liquid crystal is poured into a well-processed slotted plane, the liquid crystal molecules will be arranged along the grooves. Therefore, if those grooves are very parallel, the molecules will also be completely parallel.

2. The principle of monochrome liquid crystal display (LCD) technology is to fill liquid crystal between two planes with fine grooves. The grooves on these two planes are perpendicular to each other (intersecting at 90 degrees). That is to say, if the molecules on one plane are arranged in a north-south direction, then the molecules on the other plane are arranged in an east-west direction, and the molecules located between the two planes are forced into a 90-degree twisted state. Because light propagates along the direction of molecular arrangement, it is also twisted by 90 degrees when passing through the liquid crystal. However, when a voltage is applied to the liquid crystal, the molecules will rearrange vertically, allowing light to shine directly out without any twisting. LCD relies on polarizing filters (plates) and light itself. Natural light scatters randomly in all directions. A polarizing filter is actually a series of increasingly thin parallel lines. These lines form a network that blocks all light rays that are not parallel to them. The line of the polarizing filter is exactly perpendicular to the first one, so it can completely block the already polarized light. Only when the lines of the two filters are completely parallel or the light itself has been twisted to match the second polarizing filter can the light pass through. An LCD is precisely composed of two such mutually perpendicular polarized filters, so under normal circumstances, all light attempting to penetrate should be blocked. However, due to the fact that the space between the two filters is filled with distorted liquid crystals, after the light passes through the first filter, it will be twisted by the liquid crystal molecules by 90 degrees and finally pass through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules will rearrange and become completely parallel, preventing the light from twisting. Therefore, it is exactly blocked by the second filter. In conclusion, powering on blocks the light, while not powering it causes the light to escape. However, the arrangement of the liquid crystals in an LCD can be changed so that light is emitted when powered on but blocked when not. However, since computer screens are almost always on, only the solution of "powering on to block the light" can achieve the most power-saving goal. From the perspective of the structure of liquid crystal displays, whether it is a laptop or a desktop system, the LCD screens used are all composed of different parts in a layered structure. An LCD is composed of two glass plates, each approximately 1mm thick, separated by a uniform 5μm gap containing liquid crystal (LC) material. Since the liquid crystal material itself does not emit light, there are tubes serving as light sources on both sides of the display screen. On the back of the liquid crystal display screen, there is a backlight plate (or called a light homogenizer plate) and a reflective film. The backlight plate is composed of fluorescent substances and can emit light. Its main function is to provide a uniform background light source. The light emitted by the backlight panel passes through the first layer of polarization filter and then enters the liquid crystal layer containing tens of thousands of crystal droplets. The crystal droplets in the liquid crystal layer are all contained within tiny cell structures, and one or more cells form a pixel on the screen. Between the glass plate and the liquid crystal material are transparent electrodes, which are divided into rows and columns. At the intersection points of the rows and columns, the optical rotation state of the liquid crystal is changed by altering the voltage. The function of the liquid crystal material is similar to that of small light valves. Around the liquid crystal material are the control circuit section and the drive circuit section. When an electric field is generated by the electrodes in an LCD, the liquid crystal molecules will be distorted, thereby refracting the light passing through them in a regular manner. Then, after being filtered by the second filter layer, the light is displayed on the screen.

3. The working principle of color LCD displays: For more complex color displays that are required for laptops or desktop LCD displays, they also need to have a dedicated color filter layer for color display processing. Typically, in a color LCD panel, each pixel is composed of three liquid crystal cells, and each cell has a red, green, or blue filter in front of it respectively. In this way, the light passing through different cells can display different colors on the screen. LCD overcomes the shortcomings of CRT such as large size, high power consumption and flickering, but it also brings problems such as high cost, limited viewing Angle and unsatisfactory color display. CRT displays offer a range of resolutions to choose from and can be adjusted according to the screen requirements, but LCD screens only contain a fixed number of liquid crystal units and can only display at one resolution across the entire screen (each unit represents one pixel). CRT usually has three electron guns. The electron flow emitted must be precisely concentrated; otherwise, a clear image display cannot be achieved. However, LCDS do not have the focusing problem because each liquid crystal unit is switched on and off separately. This is precisely why the same picture is so clear on an LCD screen. LCDS do not need to be concerned about refresh rate and flicker either. The liquid crystal units are either on or off, so the images displayed at a low refresh rate of 40 to 60Hz will not flicker more than those displayed at 75Hz. However, the liquid crystal units of LCD screens are prone to defects. For a 1024×768 screen, each pixel is composed of three units, each responsible for the display of red, green and blue respectively - so a total of approximately 2.4 million units are needed (1024×768×3 = 2,359,296). It is very difficult to ensure that all these units are intact. Most likely, some of them have already been short-circuited (with a "bright spot") or open-circuited (with a "black dot"). So, it's not the case that such expensive display products won't have any flaws. The LCD display screen incorporates some elements that have never been used in CRT technology. The light source for the screen is provided by the fluorescent tubes coiled around its back. Sometimes, you may notice abnormally bright lines in a certain part of the screen. Some unseemly stripes may also appear. A special light or dark image can affect the adjacent display area. In addition, some rather precise patterns (such as images that have undergone jitter processing) may show unsightly ripples or interference patterns on the LCD screen. Nowadays, almost all LCDS applied in notebook or desktop systems use thin-film transistors (TFTS) to activate the cells in the liquid crystal layer. TFT LCD technology can display clearer and brighter images. Early LCDS, being non-active light-emitting devices, had low speed, poor efficiency and small contrast. Although they could display clear text, they often produced shadows when showing images quickly, which affected the display effect of videos. Therefore, they are now only used in PDAs, pagers or mobile phones that require black-and-white display. With the rapid development of technology, LCD technology is also constantly evolving and improving. At present, major LCD display manufacturers are all increasing their R&D expenses for LCDS, striving to break through the technical bottlenecks of LCDS, further accelerate the industrialization process of LCD displays, reduce production costs, and achieve a price level that users can accept.