A computer monitor (display) is a device designed to display text and graphic information on a screen. Of course, a monitor is an important part of a personal computer, but it is important for a person, and not for the operation of the computer itself.
By type of internal device (technology) monitors are divided into:
- CRT – based on a cathode ray tube (born CRT – cathode ray tube)
- LCD – liquid crystal monitors (born LCD – liquid crystal display)
By type of interface cable in monitors are divided into:
- D-sub
- DVI
- HDMI
Contents
CRT monitors
CRT monitors (Cathode Ray Tube) – now almost completely disappeared from store shelves. As the name implies, all such monitors are based on a cathode ray tube, but this is a literal translation, it is technically correct to say a cathode ray tube (CRT). Sometimes CRT stands for Cathode Ray Terminal, which corresponds not to the handset itself, but to the device based on it.
The technology used in this type of monitor was developed by German scientist Ferdinand Brown in 1897. and was originally created as a special tool for measuring alternating current, that is, for an oscilloscope. The most important element of a monitor is a picture tube, also called a cathode ray tube. The kinescope consists of a sealed glass tube, inside of which there is a vacuum, that is, all air is removed. One of the ends of the tube is narrow and long – this is the neck, and the other – wide and fairly flat – this is the screen. On the front side, the inside of the tube glass is coated with a phosphor (luminophor). As phosphors for non-ferrous CRTs, rather complex compositions based on rare-earth metals — yttrium, erbium, etc., are used. Phosphor is a substance that emits light when it is bombarded by charged particles. To create an image in a CRT monitor, an electron gun is used, from where, under the influence of a strong electrostatic field, a stream of electrons emanates. Through a metal mask or grill, they fall on the inner surface of the glass screen of the monitor, which is covered with multi-colored phosphor dots.
The flow of electrons (beam) can be deflected in the vertical and horizontal plane, which ensures its successive hit on the entire field of the screen. The deflection of the beam occurs through a deflection system. Deviation systems are divided into saddle-toroidal and saddle-shaped. The latter are preferable because they create a reduced level of radiation. The deflection system consists of several inductors located at the neck of the tube. Using an alternating magnetic field, two coils create a deflection of the electron beam in the horizontal plane, and the other two in the vertical. Since these monitors are no longer used on a large scale, it does not make sense to consider in more detail.
LCD monitors
History of liquid crystals
LCD screens (Liquid Crystal Display, liquid crystal monitors) are made of a substance (cyanophenyl), which is in a liquid state, but at the same time has some properties inherent in crystalline bodies. In fact, these are liquids with anisotropy of properties (in particular, optical) associated with ordering in the orientation of molecules. Oddly enough, liquid crystals are almost ten years older than CRT; the first description of these substances was made back in 1888. However, for a long time no one knew how to put them into practice: there are such substances and everything, and no one but physicists and chemists, they were not interesting. So, liquid crystal materials were discovered back in 1888 by the Austrian scientist F. Renitzer, but only in 1930, researchers from the British corporation Marconi received a patent for their industrial use. However, it didn’t go further than this, since the technological base at that time was still too weak. The first real breakthrough was made by scientists Fergason (Fergason) and Williams (Williams) from the corporation RCA (Radio Corporation of America). One of them created a temperature sensor based on liquid crystals using their selective reflective effect, the other studied the effect of an electric field on nematic crystals. And at the end of 1966, RCA Corporation demonstrated a prototype LCD monitor – a digital watch. another studied the effects of an electric field on nematic crystals. And at the end of 1966, RCA Corporation demonstrated a prototype LCD monitor – a digital watch. another studied the effects of an electric field on nematic crystals. And at the end of 1966, RCA Corporation demonstrated a prototype LCD monitor – a digital watch.
Sharp Corporation played a significant role in the development of LCD technology. She is still among the technological leaders. The world’s first calculator CS10A was produced in 1964 by this particular corporation. In October 1975, the first compact digital watch was manufactured using TN LCD technology. In the second half of the 70s, the transition began from eight-segment liquid crystal indicators to the production of matrices with the addressing of each point. So, in 1976, Sharp released a black-and-white TV with a screen diagonal of 5.5 inches, made on the basis of an LCD matrix with a resolution of 160×120 pixels.
The principle of operation of LCD screens
The operation of liquid crystal matrices is based on such a property of light as polarization. Ordinary light is unpolarized, i.e. the amplitudes of its waves lie in a huge number of planes. However, there are substances that can transmit light from only one plane. These substances are called polarizers, because the light transmitted through them becomes polarized in only one plane. If we take two polarizers, the polarization planes of which are located at an angle of 90 ° to each other, light cannot pass through them. If we place something between them that can rotate the light polarization vector by the desired angle, we will be able to control the brightness of the glow, turn off and light the light as we want. Such, in brief, is the principle of operation of the LCD matrix.
- halogen backlight
- a system of reflectors and polymer fibers, providing uniform illumination
- polarizer filter
- a glass substrate plate on which contacts are applied
- liquid crystals
- another polarizer
- again a glass substrate with contacts.
LCD Matrix Structure
In color matrices, each pixel is formed of three colored dots (red, green and blue), so a color filter is also added. At each point in time, each of the three matrix cells that make up one pixel is either on or off. Combining their states, we get shades of color, and including all at the same time – white. Globally, matrices are divided into passive (simple) and active. In passive matrices, control is performed pixel by pixel, i.e. in order from cell to cell in a row. The problem that arises in the production of LCD screens using this technology is that when the diagonal is increased, the lengths of the conductors along which the current is transmitted to each pixel are increased. Firstly, until the last pixel is changed, the first one has time to lose its charge and go out. Secondly, a longer length requires more voltage, which leads to an increase in interference and interference. This dramatically degrades picture quality and color accuracy. Because of this, passive matrices are used only where a large diagonal and a high display density are not needed. To overcome this problem, active matrices have been developed. The basis was the invention of technology known to everyone by the abbreviation TFT, which means Thin Film Transistor – a thin-film transistor.
Thanks to TFT, it became possible to control each pixel on the screen separately. This drastically reduces the reaction time of the matrix and makes possible large diagonals of the matrices. Transistors are isolated from each other and brought to each cell of the matrix. They create a field when they are ordered by the control logic – the matrix driver. In order for the cell not to lose charge prematurely, a small capacitor is added to it, which plays the role of a buffer capacity. Using this technology, it was possible to drastically reduce the reaction time of individual matrix cells.
Matrix Types
The differences between different types of matrices are due to the location of the liquid crystals and, as a consequence, the features of the passage of light through them. TN + film Crystals in a TN-matrix The first and most simple matrix production technology was TN (Twisted Nematic, twisted nematic) technology, introduced back in 1973. A feature of nematic crystals is that they line up one after another, like soldiers in a column. Organizing them in a matrix looks like a spiral. To do this, special grooves are made on glass substrates, thanks to which the first crystal in the spiral is always located in the same plane. The crystals following it are arranged one after another in a spiral until the last one fits into a similar groove on the second substrate, located at an angle of 90 ° to the first. Electrodes are connected to each end of the spiral, which influence the arrangement of crystals by creating an electric field. In the absence of voltage and field, the crystals rotate the axis of polarization of the light transmitted through the first polarizer by 90 ° so that it turns out to be in the same plane with the second polarizer and freely passes through it. This results in a white pixel. If voltage is applied to the electrodes, the coil begins to contract. The maximum voltage value corresponds to a position in which the crystals do not rotate the polarized light, and it is absorbed by the second polarizer (black pixel). To obtain gradations (shades of gray), the voltage varies, then the crystals occupy a position in which the light does not pass through the filters completely. In the absence of voltage and field, the crystals rotate the axis of polarization of the light transmitted through the first polarizer by 90 ° so that it turns out to be in the same plane with the second polarizer and freely passes through it. This results in a white pixel. If voltage is applied to the electrodes, the coil begins to contract. The maximum voltage value corresponds to a position in which the crystals do not rotate the polarized light, and it is absorbed by the second polarizer (black pixel). To obtain gradations (shades of gray), the voltage varies, then the crystals occupy a position in which the light does not pass through the filters completely. In the absence of voltage and field, the crystals rotate the axis of polarization of the light transmitted through the first polarizer by 90 ° so that it turns out to be in the same plane with the second polarizer and freely passes through it. This results in a white pixel. If voltage is applied to the electrodes, the coil begins to contract. The maximum voltage value corresponds to a position in which the crystals do not rotate the polarized light, and it is absorbed by the second polarizer (black pixel). To obtain gradations (shades of gray), the voltage varies, then the crystals occupy a position in which the light does not pass through the filters completely. so that it is in the same plane with the second polarizer and freely passes through it. This results in a white pixel. If voltage is applied to the electrodes, the coil begins to contract. The maximum voltage value corresponds to a position in which the crystals do not rotate the polarized light, and it is absorbed by the second polarizer (black pixel). To obtain gradations (shades of gray), the voltage varies, then the crystals occupy a position in which the light does not pass through the filters completely. so that it is in the same plane with the second polarizer and freely passes through it. This results in a white pixel. If voltage is applied to the electrodes, the coil begins to contract. The maximum voltage value corresponds to a position in which the crystals do not rotate the polarized light, and it is absorbed by the second polarizer (black pixel). To obtain gradations (shades of gray), the voltage varies, then the crystals occupy a position in which the light does not pass through the filters completely.
The principle of operation of LCD matrices by the example of TN
Due to the nature of TN, the clear formation of shades is very difficult, and to this day color rendering is their Achilles heel. The problem with the first TN-matrices was very small viewing angles at which the cell was visible with the desired color. Therefore, a special film was developed, which is superimposed on top of the matrix and expands the viewing angles. The technology became known as TN + film. In this performance, it exists to this day. Explain it. The angle between the normal of the front of the light wave and the angle of the director of the LC molecules (the very grooves are so scientifically called) is j. The intensity of the light transmitted through 2 polarizers is equal to sin2 j. From a practical point of view, these constructions mean that when the pixel is fully turned on, the angle j is not more than 30 °, and the light intensity varies within 10%. But in the middle position at a gray level of 50%, the angle j will be 45 °, and the intensity change will be about 90%. Naturally, it is unlikely that anyone will be satisfied that, having moved on a chair, he will see green instead of red. Therefore, a film with a different value of j is glued on top of the matrix, because of which the change in intensity when changing the viewing angle is no longer so noticeable. Today’s matrices provide a normal image with a deviation from the center of about 50-60 ° horizontally (viewing angle 100-120 °), but with vertical angles, the situation is worse. If you deviate from the center vertically at least 30 degrees, the lower part of the matrix begins to lighten, sometimes dark bands appear, etc. Therefore, a film with a different value of j is glued on top of the matrix, because of which the change in intensity when changing the viewing angle is no longer so noticeable. Today’s matrices provide a normal image with a deviation from the center of about 50-60 ° horizontally (viewing angle 100-120 °), but with vertical angles, the situation is worse. If you deviate from the center vertically at least 30 degrees, the lower part of the matrix begins to lighten, sometimes dark bands appear, etc. Therefore, a film with a different value of j is glued on top of the matrix, because of which the change in intensity when changing the viewing angle is no longer so noticeable. Today’s matrices provide a normal image with a deviation from the center of about 50-60 ° horizontally (viewing angle 100-120 °), but with vertical angles, the situation is worse. If you deviate from the center vertically at least 30 degrees, the lower part of the matrix begins to lighten, sometimes dark bands appear, etc.
Another feature of TN is that the default pixel position (i.e., when the current on the electrodes is off) is white. In this case, if the transistor burns out, we always get a brightly burning dot on the monitor. And taking into account that it is impossible to achieve absolutely accurate crystal position, it is impossible to achieve a good black display on TN matrices. Due to the limited speed of passive matrices, STN (Super Twisted Nematic) technology was developed to reduce the reaction rate. Its meaning is that the grooves on the glass substrates, orienting the first and last crystal, are located at an angle of more than 200 ° to each other, and not 90 °, as in ordinary TN. In this case, the transition between the extreme states is sharply accelerated, but it becomes extremely difficult to control the crystals in the middle positions. They were more or less stable at angles between grooves of about 210 °. However, it was not without drawbacks here: when deviating from the center of the cell, the white light became either dirty yellow or bluish. In order to somehow alleviate this problem, Sharp engineers developed the DSTN – Dual-Scan Twisted Nematic. The essence of the technology is that the screen is divided into two parts, each of which is controlled separately. In addition to increasing speed, the advantage of the technology was the mitigation of color distortions, and the disadvantage was the large weight and high cost. The essence of the technology is that the screen is divided into two parts, each of which is controlled separately. In addition to increasing speed, the advantage of the technology was the mitigation of color distortions, and the disadvantage was the large weight and high cost. The essence of the technology is that the screen is divided into two parts, each of which is controlled separately. In addition to increasing speed, the advantage of the technology was the mitigation of color distortions, and the disadvantage was the large weight and high cost.
S-IPS matrix
Hitachi decided not to deal with TN’s flaws, but simply use a different technology. Gunter Baur’s discovery dating back to 1971 was taken as the basis. The developed technology is called Super-TFT, and when commercialized – IPS (In-Plane Switching). The fundamental difference between this technology and TN consists in the arrangement of crystals: they are not twisted into a spiral, but are located parallel to each other along the plane of the screen. Both electrodes are on the bottom glass substrate. In the absence of voltage at the electrodes, light is not passed through the second polarizing filter, the plane of polarization of which is located at an angle of 90 ° to the first.
Thus, IPS provides at times better contrast, and the black color remains black, not dark gray. In addition, viewing angles are 170 ° both horizontally and vertically. The disadvantages of the technology are due to its advantages.
- First, it takes time to rotate the entire array of parallel crystals. Therefore, the reaction time for monitors based on IPS, as well as the evolutionary extensions of this technology, S-IPS (Super-IPS) and DD-IPS (DualDomain-IPS) is longer than that of TN + film. The average value for this type of matrix is 35-25 ms.
- Secondly, the location of the electrodes on the same substrate requires more voltage to create a sufficient field to rotate the crystals to the desired position. Therefore, IPS-based monitors consume more power. Thirdly, more powerful lamps are required to illuminate the panel and at the same time provide sufficient brightness.
- Fourth, these panels are corny expensive, and until recently they were installed only in monitors with large diagonals. In short, monitors based on this type of matrix remain an ideal choice for designers and other professionals whose work is critical to color rendering quality and uncritical to cell switching speed.
MVA / PVA matrix
Since it became practically impossible to deal with the disadvantages of TN + film, and it was simply unrealistic to increase the speed of S-IPS, Fujitsu developed and introduced VA (Vertical Alignment) technology in 1996. For commercial use, however, this technology was not suitable and was developed to MVA (Multi-Domain Vertical Alignment). The technology was supposed to compromise between TN speed and S-IPS image quality. Therefore, the implementation is largely similar to IPS. In these matrices, crystals are arranged parallel to each other and at an angle of 90 ° to the second filter. Thus, the light enters the second filter with the axis of polarization directed at an angle of 90 ° to the plane of polarization of the filter, and is absorbed. As a result, we get an unlit black color on the screen.
By applying voltage to the cell, we rotate the crystals and get a luminous pixel. The disadvantage of the first VA matrices was that the color changed dramatically when changing the viewing angle horizontally. In order to understand this phenomenon, imagine that the crystals are rotated 45 degrees and show a light red color. Now we are shifting to one side. The viewing angle is growing, and we get a much more saturated red color. Moving in the opposite direction, we see how the color goes into the opposite part of the spectrum and turns green. Therefore, MVA was developed. Its essence is that the polarization filters were significantly complicated, and not just flat electrodes, but peculiar triangles began to be applied to the glass substrate.
MVA structure
When the current is off, the crystals always line up perpendicular to the substrate, so that no matter which side we look, there will always be black. When the current is turned on, as always, the crystals rotate by the desired angle and rotate the light polarization vector. That’s just this angle – between the plane of the electrode and the crystal. If we look at an angle, we will always see only one zone, the crystals in which are located just in this position so as not to distort the color. The second zone will not be visible. The right color at any angle. This solution greatly complicates both the polarizer filters and the panels themselves, because each point on the screen needs to be duplicated for two zones. As with S-IPS, MVA’s weaknesses are due to its merits. There is still the same inertia – the response time is higher than that of TN. However, at the moment the difference is already absolutely uncritical: value reached 8 ms. Contrast and brightness are much better than S-IPS, up to 1000: 1. The color rendering of MVA matrices is considered a compromise between TN and S-IPS: it is not so good as to be used for serious work with printing and design, but it far exceeds the creepy performance of TN + film.
Samsung did not want to pay Fujitsu royalties and developed PVA. However, these technologies are very similar, but the differences are insignificant. The only significant thing is the high contrast, which is only a plus. Therefore, quite often in the characteristics of the monitor in the column “matrix type” write MVA / PVA.
Comparison of LCD types
Parameters of LCD monitors Despite the fact that the response time of the cell is far from the most important indicator, most often when choosing a monitor, the buyer pays attention only to this factor. Actually, that’s why TN + film dominates. However, when choosing a specific model, you should carefully consider all the characteristics of the monitor. Response Time This indicator indicates the minimum time that the cell of a liquid crystal panel changes color. There are two ways to measure matrix speed: black to black, black-white-black, and gray to gray, between grayscale. These values are very different. When the state of the cell changes between the extreme positions (black-white), the maximum voltage is applied to the crystal, so it rotates at maximum speed. This is how the values obtained in 8, 6,
When crystals are shifted between gray gradations, a much lower voltage is applied to the cell, because you need to position them precisely to obtain the desired shade. Therefore, much more time is spent for this (for matrices 16 ms – up to 27-28 ms). Only recently in the final products were able to implement a reasonably logical way to solve this problem. The maximum voltage is applied to the cell (or is reset to zero), and at the right time it is instantly displayed at the time necessary to maintain the position of the crystal. The difficulty is the precise control of voltage with a frequency exceeding the sweep frequency. In addition, the momentum must be calculated taking into account the initial position of the crystals. However, Samsung has already introduced models with Digital Capacitance Compensation technology, which provides 8-6 ms for PVA matrices.
Contrast
The contrast value is determined by the ratio of the brightness of the matrix in the state of “black” and “white”. Those. the less black is illuminated and the higher the brightness of white, the higher the contrast. This indicator is critical for watching videos, images and, in principle, for a good display of any image. It looks like, for example, 250: 1, i.e. the brightness of the matrix in the “white” state is 250 cd / m2, and in the “black” state is 1 cd / m2 2. However, such values are possible only in the case of TN + film, for S-IPS the average value is 400: 1, and for PVA – up to 1000: 1. However, the values declared in the characteristics of the monitor should be trusted only with a stretch, because this value is measured for the matrix, and not for the monitor. And it is measured on a special stand, when a strictly standard voltage is applied to the matrix, the backlight is powered by a strictly standard current, etc.
Brightness
Measured in cd / m 2. It is important for working with images, for colorful games and videos. Depends on the power of the backlight and, indirectly, on the type of matrix (remember the disadvantages of S-IPS?).
Viewing angles
Typically, values of 170 ° / 170 ° are indicated, however, for TN + film this value is no more than a declaration. A requirement in determining viewing angles is to maintain a contrast of at least 10: 1. At the same time, color rendering in this position is absolutely indifferent, even if the colors are inverted. We also take into account that the angles are determined in the center of the matrix, and we naturally look at angles from an angle.
Color rendering
Prior to crossing the 25 ms boundary, when switching the cell in black-white-black order, all TN matrices displayed an honest 24-bit color. However, in the speed race AU Optronics decided to discard the honest color rendition. Starting from matrices with a speed of 16 ms, all TN + film provide only 262 thousand shades (18 bits). A greater number of shades is provided in two ways: either by mixing dots with different colors (dithering), or by changing the color of the cell each time the picture is updated (Frame Rate Control, FRC). The second way is “more honest”, because the human eye still does not have time to notice color changes in each frame. We emphasize that only TN + film matrices are 18-bit, matrices produced using other technologies support 24-bit color rendering.
Backlight module
Based on fluorescent lamps
Through the panel body (polarizers, electrodes, color filters, etc.), only a small part of the initial luminous flux from the backlight passes, not more than 3%. Therefore, the intrinsic brightness of the backlight module should be quite significant – as a rule, the lamps used have a brightness of over 30,000 cd / m2. About 3% of the luminous flux passes through the LCD panel.
For illumination, CCFL fluorescent lamps with a cold cathode (without cathode filaments) are used. The CCFL lamp is a sealed glass tube filled with an inert gas with a small admixture of mercury. The cathodes in this case are equal electrodes, since AC is used for power supply. Compared to incandescent (hot) cathode tubes, the electrodes of u have a different structure and larger size. The working temperature of the cathode is significantly different: 80-150 ° C versus approximately 900 ° C for lamps with a hot cathode, at a close temperature of the lamp itself – 30-75 ° C and 40 ° C, respectively. The operating voltage for CCFL is 600-900 V, the starting voltage is 900-1600 V (the figures are rather arbitrary, since the range of lamps used is very wide). The formation of light occurs during gas ionization, and a necessary condition for its occurrence in a lamp with a cold cathode is a high voltage. Therefore, to start such a lamp, it is required for several hundred microseconds to apply a voltage significantly higher than the working voltage to the electrodes. Applied high alternating voltage causes gas ionization and breakdown of the gap between the electrodes, a discharge occurs.
Breakdown of the discharge gap occurs for the following reasons. Under normal conditions, the lamp-filling gas is an insulator. When an electric field appears, a small amount of ions and electrons, always present in the gas volume, starts to move. If a sufficiently high voltage is applied to the electrodes, the electric field gives the ions such a high speed that when they collide with neutral molecules, they knock electrons out of them and form ions. The newly formed electrons and ions, moving under the influence of the field, also enter into the ionization process, the process assumes an avalanche-like character. After the ions begin to receive enough energy to knock electrons by striking the cathode, an independent discharge occurs. Unlike hot cathode tubes, where the discharge is an arc,
The maximum color gamut could ideally be provided by a combination of monochromatic sources of primary colors and high-quality color filters. The so-called laser LEDs may claim the role of “quasimonochromatic” light sources, but the production technology does not yet ensure the profitability of their use in backlight modules. Therefore, at the moment, the best color gamut allows you to achieve backlight modules based on RGB LED packages.
To generate a voltage of several hundred volts required for the operation of the lamps, special converters are used – inverters. CCFL brightness adjustment is carried out in two ways. The first is to change the discharge current in the lamp. The current value in the discharge is 3-8 mA, a significant part of the lamps has an even narrower range. At a lower current, the illumination uniformity suffers, with a larger current, the lamp life is significantly reduced. The disadvantage of this adjustment method is that it allows you to change the brightness in a very small range, its significant reduction is impossible. Therefore, monitors with this adjustment when working in low ambient light are often too bright even at zero brightness. In the second method, pulse-width modulation (PWM) of the supply voltage lamp is generated (the width, i.e., the pulse width, is controlled by changing the width of a single pulse to regulate the average voltage level.). The disadvantages of this method are sometimes attributed to the appearance of flickering of lamps during the implementation of PWM at a low frequency of 200 Hz and lower, in fact, adjustment using PWM is the most reasonable approach, since it allows you to change the brightness over a wide range.
A system of optical fibers, diffusers and prisms is used to evenly distribute the light of the lamps. There are many options for organizing the distribution of light. Solutions with the arrangement of lamps on the upper and lower end sides of the panel are the most common, this arrangement can significantly reduce the overall thickness of the product. In 17- and 19-inch modules, as a rule, four lamps are installed: two on the upper side and two on the lower. There are special technological holes in the end part of the case of such panels, therefore, it is not necessary to disassemble the case to remove the lamps. Lamps with this arrangement are often combined in blocks of two pieces. Another option is the location of the lamps over the entire area of the reverse side of the module — this solution is used in multi-tube panels with eight or more lamps,
LED based
In addition to fluorescent lamps, light emitting diodes (LEDs) can also be used. The backlight modules based on LEDs are built either on “white” LEDs or on packages of LEDs in primary colors (RGB-LED). The greatest color gamut give packages RGB-LED. The fact is that the “white” LED is a blue LED with a yellow phosphor coating, or an ultraviolet LED with a combination of “red”, “green” and “blue” phosphor coating. The spectrum of “white” LEDs is not free from all the shortcomings of the spectrum of fluorescent lamps. In addition, unlike the “white” LEDs, the RGB-LED package allows you to adjust the color temperature of the backlight online by separately controlling the intensity of the glow of each group of LEDs in the primary colors. As a result, two goals are achieved: – color gamut is expanded due to a more ideal backlight spectrum; – color calibration options are expanded: the standard method based on color coordinate conversion tables for image pixels adds the ability to adjust the color balance of the backlight. The large steepness of the current-voltage characteristics of LEDs does not allow smoothly adjusting the brightness of radiation in wide ranges. But since the device allows operation in a pulsed mode, in practice, the method of pulse-width modulation is most often used to adjust the brightness of LEDs (as well as for fluorescent lamps). to the standard method based on color coordinates conversion tables for image pixels, the ability to adjust the color balance of the backlight is added. The large steepness of the current-voltage characteristics of LEDs does not allow smoothly adjusting the brightness of radiation in wide ranges. But since the device allows operation in a pulsed mode, in practice, the method of pulse-width modulation is most often used to adjust the brightness of LEDs (as well as for fluorescent lamps). to the standard method based on color coordinates conversion tables for image pixels, the ability to adjust the color balance of the backlight is added. The large steepness of the current-voltage characteristics of LEDs does not allow smoothly adjusting the brightness of radiation in wide ranges. But since the device allows operation in a pulsed mode, in practice, the method of pulse-width modulation is most often used to adjust the brightness of LEDs (as well as for fluorescent lamps).