Choosing a monitor without shim. Why do computer (monitor) eyes hurt? Pulse width modulation on monitors

Looking for flicker-free AMOLED (PWM) (updated periodically) July 25th, 2017

I want to buy a smartphone, does it flicker?
TFT (as well as IPS, PLS, Super LCD) in 99% of cases does not flicker, or flickers at a high frequency (completely invisible to the eye).
You can also look for reviews of the model you are interested in on sites that conduct PWM tests: S8+ and S7 Edge, in which ripple is reduced to nothing at any brightness. The only drawback that the author writes about is that at minimum brightness the mura defect begins to appear A Japanese word for defect that is adapted in English to name defects in the pixel matrix of a display surface that are noticeable at a specified constant gray level of the display screen.

What now, don't buy Samsung?
If you are going to read books on it, I don’t recommend it. In other cases, you may not notice anything serious. Here are some thoughts:
The flickering coefficient of CRT televisions (which have been used for more than one generation) can easily reach 250%, but hardly anyone tried to read Tolstoy’s “War and Peace” on them.
It is perhaps no coincidence that I measured the highest flicker on large AMOLED displays (5.5 inches or more). What if hygienists (if there are such specialists on Samsung's staff) know that a user of a relatively high-flicker, but large display, gets about the same fatigue as a user of a small display with less flicker?

There are a huge number of ways to check the quality of a monitor or TV before purchasing. In stores, consultants always focus the buyer’s attention on size and resolution.

But most experienced, advanced buyers are confident that checking the screen for PWM flicker using a regular pencil or pen allows you to avoid buying a low-quality monitor that will be harmful to your health.

What is PWM

PWM or Pulse Width Modulation is one method of reducing the perceived brightness of a monitor or TV screen. The flickering effect is created by regularly delivering pulses at a predetermined purity. At the same time, the screen backlight turns on and off at a very fast speed. It is quite difficult to notice such an effect on your own.

It is worth noting that the higher the flicker frequency, the more difficult it will be for a person to work on a laptop or computer.

It is used to achieve a wide range of brightness control. According to experts, this is one of the most convenient and easiest ways to achieve this goal.

Any object that is a light generator produces a flickering effect. The exception is incandescent lamps.

The legislation of the Russian Federation stipulates that the flicker coefficient in the workplace should not exceed 10-20% at a frequency below 300 Hz.

Despite the fact that pulse width modulation operates at a standard frequency of 175 Hertz, this can lead to noticeable negative changes in the performance of the monitor.

Why you need to check for flicker

First of all, the main task when testing flicker is to purchase quality equipment. According to programmers, if the monitor flickers regularly and continuously, then a person who uses it for work for a long time may experience severe fatigue and other signs of illness, for example:

• This affects the health of our eyes. Since they are constantly tense from constant pulsation, vision may noticeably deteriorate;
• Also, one of the signs of constant pulsation of the monitor is the appearance of headaches and drowsiness. In this state, it is very difficult for a person to concentrate on his work.

Therefore, despite the fact that a reliable device that will not harm your health will cost several times more, it is worth giving preference to it.

In order to check your monitor screen for flickering, which is created by PWM, you must:

• Use a regular pencil or pen;
• After this, find a very light picture, preferably white. If you don't have access to the Internet, you can open any text editor, such as Notepad, and open a blank, full-width document. The main thing is that most of the screen is white;
• Then take your pencil or any long and thin object;
• Next, rotate it in a semicircle 10-15 cm from the screen.

If the outline of the pencil is practically invisible to you, then the flickering of the screen is minimal. This means that the screen quality of your monitor is quite good. When working for a long time, you will not feel tired and tense in your eyes and body.

If the contour is visible clearly enough, then the pulsation of light from the screen is very large. Therefore, it is necessary to take measures to eliminate this problem.

How to remove flicker

Experts say that the only way to fix this problem is to completely replace the screen with a new one. At the same time, there is an opinion that it is possible to reduce PWM - ripple by reducing the flicker frequency in the settings. In this case, it will be easier for the user to work at the computer.

There is also an alternative way to reduce the ripple effect:

• To start, set your screen brightness to maximum;
• Next, check that the “Auto Configuration” function is disabled;
• And after that, you need to find the color correction or contrast adjustment on the video card driver and reduce it to normal;
• In this way, we reduce the brightness and contrast of the screen, and the backlight of your screen allows your eyes to ignore all the flicker.

It is worth noting that this effect will not last long. Therefore, if you care about your health, it is best to purchase a monitor that does not have pulse width modulation. For example, an excellent option would be a screen whose brightness control method has a height several times greater than PWM.

How they FOOL YOU when selling MONITORS and TV. DISCLOSURE:

In the previous article you learned. As a continuation, I propose to find out what PWM is in monitors, how to live with it and not damage your eyes.

Be careful, they flicker!

Everyone is accustomed to the idea that only old large cathode ray tube (CRT) monitors flicker, but in fact, the flickering of modern LCD and OLED displays is much more harmful to the eyes!

Yes, you didn't think so Most modern displays flicker and this flickering usually appears when brightness decreases.

Look at this animation, the left brightness symbol flickers unpleasantly at 50% level

And this can be observed not only on desktop computer monitors, the same thing happens with many laptops, smartphones and tablets.

What is PWM in monitors?

There are two ways to lower the brightness of your monitor:

a.) Reduce the intensity of the backlight lamp (the lamp reduces the glow)
b.) Shine intermittently so that there is less light per unit of time (the lamp begins to flicker)

From a technical point of view, it turned out to be easier to make the brightness adjustable by flickering, Part of the time the lamp is on, and part of the time it is off.

Pulse width modulation (PWM)- the process of power control by changing the pulse duration at a constant frequency.

In monitors with PWM when the screen brightness decreases the duration of the glow pulse of backlight lamps or LEDs decreases, as a result flicker is more noticeable, which can negatively affect our vision.

In the figure you can see a comparison of two ways to adjust brightness:

PWM works as follows: at 50% brightness, half the time we see a pulse of light, and the second half of the time we see a black screen, the eye averages what it sees and we perceive a gray glow. When the brightness is lower, the flicker is noticeably greater.

But such flickering is not at all good for the eye.

Do all monitors flicker?

Manufacturers are in no hurry to indicate in the specifications how brightness is adjusted and whether PWM is used. Fortunately, There are monitors that do not have PWM, or flickering appears at a very low brightness.

Such monitors sometimes have the inscription in the description "Flicker-Free"(translated as “no flicker”) and a similar logo appears:

Before purchasing, you can study specialized forums in search of the desired model, but what to do if you have already bought a monitor that flickers?

How to tell if your monitor is flickering?

There is a very simple way to find out if your monitor is flickering - " pencil test».

Take the pencil in your hands and move it in front of the glowing monitor like a fan (in the plane of the screen). If the pencil mark is blurry(looks blurry) then no flickering, if the trail splits(looks like a set of shadows from several pencils), then your monitor is flickering.

This video shows an example of the “pencil test”:

Test at different brightness levels, from 0% to 100%, so you can find out what brightness is safe for your eyesight.

There are more complex tests that allow you to find out the flicker frequency, but in most cases the pencil test is sufficient.

What should I do if my monitor flickers?

If you find that your monitor is flickering at a comfortable brightness level, there is a way to avoid damaging your eyes:

Adjust brightness using your video card driver

The image quality may be a little worse, but it will be much easier on the eyes.

You need to adjust the brightness of the monitor so that there is no flickering, and if in the end the brightness is too high, reduce the brightness in the video card driver settings.

The setup algorithm is simple:

1. Adjust your monitor brightness to either maximum or a flicker-free level;
2. Go to the video adapter driver settings and reduce the brightness to a comfortable level;
3. Apply the settings.

Brightness setting example

If you have any difficulties finding driver settings, write in the comments, I will try to help.

Conclusion

Today you learned what is PWM, why is it dangerous for the eyes and how to minimize risks.

Write if you are interested in lessons on health and if you need details on the issues discussed in the article.

Copying prohibited, but you can share links.

Introduction

Liquid crystal displays (LCD) are used in a wide variety of environments, so it is desirable to produce displays that can be adjusted in brightness and are suitable for use in both light and dark conditions. Then the user will be able to adjust the screen to a comfortable brightness level depending on its operating conditions and general lighting.

Manufacturers usually list the display's maximum brightness in a display's specifications, but it's important to take into account the lower brightness levels at which the screen is capable of operating - since you're unlikely to want to use it at maximum brightness. Although specifications often include values ​​up to 500 cd/m², you will likely want to use the screen at a brightness that is somewhat more comfortable for your eyes.

As a reminder, in each of our reviews on tftcentral.co.uk we test the full range of backlight dimming and associated brightness values. During calibration, we also try to set the screen brightness to 120 cd/m², which is the recommended level for an LCD monitor under normal lighting conditions. This helps you get an idea of ​​how to set the brightness level at which you'll most likely want to use it on a daily basis.

Both in the case of fluorescent lamp (CCFL) and light-emitting diode (LED) backlighting, changing the display brightness is achieved by reducing the overall luminous output of the backlight. Currently, the most commonly used method to dim the backlight is pulse width modulation (PWM), which has been used in desktop and laptop displays for many years. However, this method is not without its problems, and with the advent of high-brightness displays and the proliferation of LED backlighting, the side effects of PWM have become more noticeable than before, and in some cases, PWM can cause rapid visual fatigue in people who are sensitive to it.

The purpose of this article is not to alarm you, but to tell you how PWM works, why it is used, and how to test your display to see these effects more clearly.

What is PWM?

Pulse width modulation (PWM) is a method of reducing perceived brightness in displays, working by rapidly cycling the backlight on and off. This periodic supply of pulses usually occurs at a constant frequency, and the ratio of the duration of the part of each cycle during which the backlight is on to the total duration of the cycle is called the duty cycle (the reciprocal of the duty cycle). By changing the duty cycle, a change in the overall light output of the backlight is achieved. At the visual level, this mechanism works because the backlight alternates between on and off states quickly enough that the user does not notice the flicker because it is beyond the flicker fusion threshold (more on this below).

Below you can see graphs of the light output of the backlight over several cycles using the “ideal” PWM. The maximum luminous output of the backlight in this example is 100 cd/m², and the perceived brightness for fill factors of 90%, 50% and 10% is 90, 50 and 10 cd/m², respectively. The ratio between the minimum and maximum brightness levels during one cycle is called the modulation depth and in this case is 100%. Please note that during the cycle in the example given, the backlight brightness is at its maximum.

Coeff. 90% filling Coeff. 50% filling Coeff. filling 10%

Analog (non-PWM) graphs corresponding to perceived brightness levels are presented below. There is no modulation here.

Constant brightness 90% Constant brightness 50% Constant brightness 10%

Why is PWM used?

The main reasons for using PWM are the ease of its implementation, for which the backlight only needs the ability to turn on and off frequently, as well as the wide range of possible brightness values ​​​​provided with its help.

It is possible to reduce the brightness of CCFL backlights by reducing the current flowing through the lamp, but only by about half due to their strict current and voltage requirements. This makes PWM the only simple way to achieve a wide range of dimming. A CCFL lamp is typically controlled by an inverter, switching on and off at a frequency of tens of kilohertz, which is beyond the flicker perceptible to humans. However, PWM typically operates at a much lower frequency, around 175 Hz, which can cause noticeable image artifacts.

The brightness of LED backlights can be adjusted over a wide range by changing the current passing through them, although as a result the color temperature changes slightly. This analogue approach to changing the brightness of LEDs is also undesirable due to the fact that the auxiliary circuits must take into account the heat generated by the LEDs. When turned on, LEDs heat up, which reduces their resistance and further increases the current flowing through them. This can lead to a rapid increase in current in ultra-bright LEDs and cause them to fail. By using PWM, the current can be forced to be held at a constant level during the operating cycle, resulting in the color temperature always being the same and no overcurrent occurring.

Side effects of PWM

While PWM is attractive to manufacturers for the reasons outlined above, it can also produce unpleasant visual effects if used carelessly. To understand what we're seeing, we need to look at the flicker of real displays. Below is a video of the CCFL backlight slowed down 40 times, making the flicker more visible. Graphs of changes in the brightness of RGB components during one cycle are shown directly below it. This particular display is set to its minimum brightness, which is where flickering should be most pronounced.

As can be seen from the video and the corresponding graphs, during one cycle the overall brightness changes by about 4 times. Interestingly, the color of the backlight also changes significantly during each cycle. This is most likely due to the fact that the phosphors in CCFL have different response times, in which case we can conclude that the phosphor involved in producing blue light may turn on and off faster than for other colors. The use of phosphors also means that the backlight will continue to emit light for a few milliseconds after the backlight turns off at the end of the operating cycle and provides a more constant level of light (less modulation) than would otherwise occur. Note that the time-averaged color remains unchanged.

LED backlight flicker is usually much more noticeable than CCFL backlight flicker at the same duty cycle because LEDs are able to turn on and off much more quickly and do not continue to glow after the power is turned off. This means that where the CCFL backlight showed a fairly smooth fluctuation in brightness, the LED version exhibits sharper transitions between on and off states. That is why, quite recently, the topic of PWM began to be raised on the Internet and in reviews against the backdrop of the emergence of more and more LED-backlit displays based on white LEDs (W-LEDs). As you can see below, there is no significant change in backlight color during the operating cycle.

The flickering effect is especially noticeable when the user's eyes move. In constant, flicker-free lighting (such as sunlight), the image blurs smoothly, which is how we typically perceive motion. However, when combined with a PWM light source, a person may see multiple separate screen afterimages at the same time, which can result in reduced readability and the ability to fixate on objects. From previous analysis of CCFL backlighting, we know that color distortion can also occur, even if the original image is black and white. Below are examples of what text might look like as your eyes move horizontally using different types of backlighting.

Original image Without PWM PWM with CCFL backlight PWM with LED backlight

It is important to remember that this is purely due to the backlight, and as such the display displays a static image. It is often said that humans cannot perceive more than 24 frames per second (fps), which is not true and in fact only corresponds to the approximate frame rate required to perceive continuous motion. In fact, when moving the eyes (for example, when reading), it is possible to see flicker effects at several hundred hertz. The ability to notice flicker varies greatly between individuals and even depends on the user's position relative to the display, since peripheral vision is the most sensitive.

So how often does the backlight turn on and off when using PWM? Apparently it depends on the type of backlight used. Fluorescent-based backlighting almost always switches at a frequency of 175 Hz, or 175 times per second. The flickering frequency of the LED backlight, according to various sources, ranges from 90 Hz to 420 Hz, and at lower frequencies the flickering is much more noticeable. It may seem like the frequency is too high to be noticeable, but keep in mind that 175 Hz is not much more frequent than the 100-120 Hz flicker that is typical for light bulbs connected directly to the mains.

In fact, the 100-120 Hz flickering frequency of fluorescent lamps has been associated with symptoms such as eye strain and headaches in some people. This is why high-frequency stabilizing circuits have been developed to provide almost continuous light output. Using PWM at low frequencies negates the benefits of using these improved stabilizing circuits in the backlight, since the nearly continuous light source then becomes flickering again. Additionally, it should be taken into account that low-quality or defective stabilizers in backlights based on fluorescent lamps can produce audible noise. This often occurs when using PWM, since electronics now deal with the additional frequency at which power consumption varies.

It is also important to understand the difference between flicker in cathode ray tube (CRT) displays and TFT displays with CCFL and LED backlighting. While a CRT can flicker at a low frequency of 60 Hz, only a narrow band is illuminated at any given time as the electron gun beam moves from top to bottom. With CCFL- and LED-backlit TFT displays, the entire surface of the screen lights up at the same time, which means a much larger amount of light is emitted in a short time. In some cases this can be more annoying than CRT flicker, especially at high duty cycles.

For some people, flicker as such in display backlights may be subtle and unnoticeable, but for others it is quite noticeable due to natural differences in human vision. With the increasing use of high-brightness LEDs, high PWM duty cycles have to be increasingly used to control brightness, which makes the flicker problem more pressing. Considering that users spend many hours every day looking at their monitors, shouldn't we consider the long-term effects of both perceived and unnoticed flicker?

Reducing the Side Effects of PWM

If you find PWM backlight flicker annoying or just want to see if reducing the flicker makes it easier to read, I would recommend you try the following. Set your monitor's brightness to maximum and disable all automatic brightness adjustment mechanisms. Now reduce the brightness to a normal level (usually using the contrast slider) using the color correction available in your graphics card drivers or using a calibration device. This will reduce the brightness and contrast of your monitor, keeping the backlight on for as long as possible throughout the PWM cycles. While the reduced contrast may not be a long-term solution for many, this technique can help determine the extent of the positive impact of reducing PWM usage.

A much better method, of course, would be to purchase a display that does not use PWM to control brightness, or at least uses a much higher PWM frequency. Unfortunately, it appears that no manufacturer has yet implemented PWM that operates at frequencies that are beyond the limits of perceived visual defects (probably well above 500 Hz for CCFL and above 2 KHz for LEDs). Additionally, some displays that use PWM do not have a 100% fill factor even at full brightness, causing them to flicker anyway. It is possible that some of the currently available LED backlit displays do not use PWM, but until backlight frequency and modulation are specified in the technical specifications, each individual display should be tested in person.

Verification and analysis

It would be great if there was an easy way to measure the PWM frequency of the backlight, and fortunately, a camera with manual shutter speed settings is all you need for this. Exactly how to use this method is described below.

Shooting:

1. Set the monitor to the settings you want to test.
2. (Optional) Set the white balance on the camera when only white is displayed on the screen. If this is not possible, set the white balance manually to approximately 6000K.
3. Display on the monitor a narrow white vertical stripe on a black background (1-3 dots thick will be enough). Only this image should be visible.
4. Set the shutter speed on your camera to a value between 1/2 and 1/25 seconds. To get enough light to shoot, you may need to adjust your ISO sensitivity and aperture. Make sure the strip is positioned at the focal length (fix it if necessary).
5. Hold the camera approximately 60 cm away from the monitor and perpendicular to it. Press the shutter button while slowly moving the camera horizontally relative to the screen (keep them perpendicular to each other as you move). You may need to experiment with moving the camera at different speeds.

Treatment:

1. Adjust the brightness of the resulting image so that the pattern is clearly visible.
2. Count the number of cycles captured in the image.
3. Divide this number by the shutter speed. For example, if you use a shutter speed of 1/25 second and count 7 cycles, the number of cycles per second is 25 * 7 = 175 Hz. This is the backlight flickering frequency.

Test image Photo Cut out useful fragment

The point of this technique is that by moving the camera while shooting, we turn the temporal effect into a spatial one. The only significant light source when shooting is a narrow strip on the screen, which falls on the light-sensitive matrix in the form of successive columns. If the backlight flickers, different columns will have different brightness or color values ​​based on the backlight at that particular moment in the photo.

A common problem when first trying to use this technique is that the image is too dark. Using a larger camera aperture (lower f/number) or increasing ISO sensitivity can improve the situation in this regard. Shutter speed has no effect on exposure, since we only use it to control the overall duration of the shooting. The brightness of the image can also be adjusted by changing the speed of the camera: a higher speed will produce a darker image at a higher time resolution, and a lower speed will result in a brighter image at a lower resolution.

Another common problem is unequal distances between individual stripes in the resulting image due to changes in the speed of the camera during shooting. To achieve constant speed, start moving the camera some time before the start of shooting, and finish some time after it ends.

An image that looks too flat may be due to out of focus. In some cases, this can be dealt with by pressing the shutter button halfway to focus and then continue as normal.

Additional effects may occur depending on your monitor. CCFL-based backlights often exhibit different colors at the beginning and end of each cycle, meaning that the phosphors used react at different rates. LED backlights often use a higher frequency than CCFL backlights and may require you to move the camera faster to see the cycles. Dark bars between cycles mean that the PWM duty cycle has been increased to such an extent that no light is emitted during that part of the cycle.

Dell 2007WFP (CCFL)

Brightness = 100 Brightness = 50 Brightness = 0

Using a shutter speed of 1/25 second, we can clearly see 7 cycles, which means the backlight flickers at 175 Hz. Even at full brightness there is some flicker, although it's likely small enough to be unnoticeable. At half brightness there is a slight flicker, and when the minimum brightness is reached there is much more noticeable flicker along with a color shift.

NEC EA231WMi (CCFL)

Brightness = 100 Brightness = 50 Brightness = 0

At full brightness there is no visible flicker. At half brightness, flickering and color shift become visible. At minimum brightness there is more flickering and significant color shift. At a shutter speed of 1/25 second, about 8 cycles are visible, which corresponds to a frequency of approximately 200 Hz. With a longer shutter speed, a more accurate frequency value was obtained - 210 Hz.

Samsung LN40B550 Television (CCFL)

Brightness = Max Brightness = Min

There is no option to disable automatic brightness adjustment, so the maximum and minimum brightness levels that can be easily achieved are shown. At full brightness there is no visible flicker. At minimum brightness there is a strong flicker and color shift, due to which the separation into yellow and blue components is visible. At a shutter speed of 1/25 second, only 6 cycles are visible, which means that the backlight flickers at a frequency of 150 Hz.

2009 Apple MacBook (LED)

Brightness = 100 Brightness = 50 Brightness = 0

When using a shutter speed of 1/25 second, there is no visible flicker or color shift regardless of brightness. This display does not use PWM. The cause of the striations is the image being noisy.

2008 Apple MacBook Pro (LED)

Brightness = 100 Brightness = 50 Brightness = 0

At 1/25 second there is some flickering at full brightness. At brightness 50 and 0, a very high duty cycle is used, resulting in strong flickering. This LED backlight uses a higher frequency of 420Hz, but it is still too low to eliminate flicker. There is no visible color shift across cycles.

Conclusion

As we noted at the outset, this article is not written to scare people away from modern LCD displays, but to help people become aware of the potential problem associated with PWM. With the growing popularity of white-light-emitting diode (W-LED) backlit monitors, it is likely that there will be more user complaints than older displays based on the PWM method used and ultimately the type of backlight chosen. Of course, the problems that PWM use can cause are not noticeable to everyone, and in fact I would expect that there are many more people who will never experience the symptoms described than those who will. For those suffering from side effects including headaches and eye strain, there is now at least an explanation.

Given that PWM technology has been around for a long time and successfully, and many years of its use in CCFL displays, I frankly doubt that anything will change in this regard in the near future, even with the increasing transition to LED backlight. PWM is still a reliable way to control backlight intensity and therefore offers the dimming capabilities that every user needs.

Those who are concerned about side effects or have had problems with previous displays should try to determine the PWM frequency of their new display and maybe even try to find a screen that doesn't use PWM to control backlight brightness at all. Unfortunately, we have yet to see manufacturers specify any specifications regarding the use of PWM, or its frequency at certain brightness levels, so it is difficult to judge at this time.

Setting the screen brightness to maximum is one of the possible methods to help reduce side effects due to lower duty cycle. This solution is of course not ideal since many displays have a very high factory or maximum brightness level, but it is something that may help. Controlling the brightness in software or using the video card driver can help return a more comfortable brightness, but may lead to a decrease in contrast.

This article will tell you the sequence of necessary actions in order to once and for all forget about pulse width modulation (PWM) in your monitor. You will work at the monitor with the brightness that will be comfortable for your eyes, with only one difference - the backlight of your monitor will not generate PWM. Everything is very simple! The main thing is to be able to work with a soldering iron...

Attention!

The actions presented in this article will void the warranty on the monitor. The author is not responsible for force majeure or other circumstances resulting in damage to your property used in attempts to repeat the steps below.

About pressing problems

Well, after much thought and saving money, I finally became the copyright holder of a number of Dell u2412m monitors. For those interested - revision A0, January 2013. Having read not very many forums where this monitor is discussed, I came to the conclusion that many potential buyers are concerned about the presence of PWM. Yes, indeed, in the first revisions users complained about PWM, but from the reviews it was clear that in subsequent revisions this problem was eliminated. Since I am not the copyright holder of the first revisions, as well as the electrical circuit diagram (in order to compare the differences in electronics), then from my experience I can assume that a simple banal step was taken - increasing the PWM frequency.

But nevertheless, people continue to ask, asking the same question again and again - “I’m thinking of taking the U2412M, but the presence of PWM confuses me. Tell me, will it make your eyes hurt a lot?”

As for me, after sitting at a monitor with PWM for a week, I got used to it, and I can say that it didn’t put much pressure on my eyes. Although everyone has their own body, as well as vision. Yes, in the first hours of sitting at the monitor it was unusual, but then somehow everything fell into place. But nevertheless, there were some moments that forced the eyes to strain. These moments appeared when it was necessary to jump with one’s gaze from one monitor to another. That's when I noticed the PWM. Since this feeling haunted me, I decided to look into the electronics of the monitor, namely the LED backlight driver.
Having added a modification, which I’ll tell you about below, my eyes began to perceive the picture on the monitor a little better... But I can’t say that there’s a big difference (or maybe I’m just used to it). But no matter the opinion, when I come home from work, the first sensations that my eyes experience after watching the work monitor are relaxation...

I’ll say right away that after making changes, the user still has the opportunity to use the internal mode for changing the brightness, which leads to the inclusion of PWM. In order to prevent the monitor electronics from turning on PWM, you need to set the monitor brightness to 100% and further change the brightness using a variable resistor.

A little about monitor electronics

(those who are not interested can skip it)
And so, what is the point... And the point is that the brightness adjustment did not take place according to the PWM principle, but according to the principle of changing the current passing through the backlight LEDs of the LCD monitor. Most LED driver chips offer this feature. But first, it would be nice to find out what kind of microcircuit is used to power the LED backlight in our monitor. To do this we need to disassemble it.

I will not dwell on where and what needs to be pressed, tightened, untwisted in order to disassemble the monitor. You can easily find this information on the Internet. For example here
The driver chip has been identified - OZ9998. The next step is to search for documentation for this chip. Unfortunately my searches were unsuccessful.

Since this chip is located on the power supply board, it would be nice to find a circuit for the power supply of the u2412m monitor. Which also was not successful. Somehow, thanks to one forum, we were able to find circuits that use our OZ9998 LED driver.
Here is an example of one of the schemes:

Based on the fact that all LED drivers have approximately the same structure, an analogue of our OZ9998 came to hand - this is TPS61199. But the numbers of the functional pins of the microcircuits do not correspond to each other. After reading the documentation for the TPS61199, you can determine that the pin named Iset is responsible for setting the current value through the LED line. In our OZ9998, the second leg of the chip is responsible for this functionality. The amount of current depends linearly on the resistance of the resistor, multiplied by a certain coefficient (for more detailed information, see TPS61199 datasheet). Since I don’t have documentation for OZ9998, I had to resort to practice. Without hesitation, I took the nearest variable resistor and soldered it in series to the existing one.

Thus, it was practically determined that the maximum set resistance on a variable resistor at which the brightness of the monitor backlight is minimally acceptable for vision is 100 kOhm. By changing the value of its resistance with the potentiometer, you can change the brightness of the monitor backlight. As a result, we got a change in brightness that occurs not according to the PWM principle, but according to the principle of changing the current passing through the backlight LEDs of the LCD monitor.

Pick up the instrument and hit the road

We assume that the monitor has already been disassembled (see how to disassemble the monitor):

Carefully peel off the electronics unit and disconnect the necessary cables:

The power board along with the interface board lies before our eyes.

We are interested in this area:

Increased:

Namely, the resistor that is connected to the second leg of the microcircuit.

In order not to accidentally exceed the current through the LEDs set by the manufacturer, we need to figure out how to solder it, leaving the original resistor. To do this, let’s unsolder it first.

Let's prepare a variable resistor by first setting the resistance between the terminals used to zero.

We solder back the original resistor (the one we soldered) into the slot (see the picture carefully) and our variable resistor as shown in the picture, that is, in series.

We bring the variable resistor out of the monitor body, so that when the monitor is assembled, it would be possible to adjust. I did it like this for myself:

That's all. Those wishing to check the functionality can connect the cables and test.
The video shows how I first increase the brightness using a variable resistor and then decrease the brightness. In the second part, the brightness is changed using the internal functions of the monitor.

PS
After working at the monitor for some time, I determined the brightness level at which it is convenient for me to work. I measured the resistance that was obtained on the variable resistor and soldered in a constant resistance resistor.