PWM on screens in smartphones - what is it, table

20.04.2021 50356 15

When purchasing a mobile device with an AMOLED screen, many do not even know what PWM is in a smartphone , although it is precisely this that is the main drawback of such matrices. Users then write that they feel headaches and discomfort in the eyes when using a phone with an AMOLED display for a long time. Let's take a closer look at what is meant by the abbreviation PWM, and how this process affects health.

shim



What is PWM

PWM (Pulse Width Modulation) is a technology used in phones to adjust the brightness of the display. Any screen consists of LEDs that allow you to see the image and text. It would seem that to reduce the brightness, it is enough to lower the power of the LEDs, but such manipulation most often does not work on AMOLED. Therefore, pulse-width modulation was invented. LEDs do not change their power, but start to turn on and off quickly.

pulse width modulation

PWM is present only if the brightness is reduced. The lower the brightness, the longer the time elapses between turning the LEDs on and off. At maximum screen brightness, there is no flickering because the pixels are bright and do not turn off. PWM will definitely appear if you lower the brightness by 40-50%.

You are probably wondering: how can a person not see this flicker? After all, it seems to be possible to determine when the lights on the screen light up and when they go out. Let's say right away that the human eye does not recognize flicker, even if you look closely. The fact is that the brain ceases to perceive flicker already at a frequency of 60 Hz. Therefore, it seems to a person that the LEDs are lit continuously. Alas, this still affects the state of health, but we will talk about this a little later.

flicker reduction

As you already understood, pulse-width modulation reduces the brightness of the screen, but it does this in a non-standard way. After a certain period of time, current enters the LED, and the pixel flashes brightly, and then goes out. Flashes are very fast and frequent - it is due to this very pulsation that we do not see, but it seems that the display is not so bright.

Health impact

Imagine that you are looking at a light bulb that is constantly flickering. Of course, there will be discomfort and even pain in the eyes. The same thing happens when using screens with PWM. You don't see the flicker at 60 Hz, but the brain still gets a lot of stimulation.

effects of shim on health

Some people are less affected by light pulses, others more. For example, pilots and gamers pick up flicker more strongly. If you are receptive to such a frequency, there will be a certain discomfort, namely:

  • dryness and redness of the eyes;
  • headache;
  • irritability and fatigue;
  • nausea.

Scientists have not identified significant harm from PWM. That is, the person will experience only short-term unpleasant symptoms. Does vision deteriorate? Unfortunately yes. You will not notice an instant deterioration, but if you use smartphones with PWM for several years, also reducing the brightness, your vision will definitely worsen.

Which smartphones use PWM

smartphones with shim

We found out what PWM is, but is it used in all mobile devices? No. The technology is used only on AMOLED matrices (OLED, Super AMOLED). The main feature of such displays is the presence of organic light-emitting diodes. Pixels work separately, they are not connected to each other. By the way, it is the independent functioning of the pixels that allows developers to implement the Always-on-Display mode.

In IPS screens, the structure is different: the matrix consists of two layers. These are liquid crystals and illumination. When the brightness is reduced on IPS, the LEDs simply change power, but do not flicker. AMOLED matrices do not have a backlight layer, so brightness control is only possible using pulse-width modulation.

Some people feel great discomfort from PWM. Even technologies that are supposed to reduce harm, such as DC Dimming, do not help. If the user is uncomfortable using Amoled, there is only one way out - to switch to IPS. Yes, the image quality and color reproduction will be much worse, but the eyes will stop suffering.

Rating of popular Android smartphones by flicker level

The number of light pulses differs depending on the smartphone model. The higher the flicker level, the less impact on the eyes. An absolutely safe indicator is 300 Hz and above.

300 Hz for vision

We cease to notice the ripple with the naked eye already at a frequency of 60 Hz. But up to 300 Hz, the brain still picks up impulses and is constantly in an excited state, which is fraught with poor health. If the frequency exceeds 300 Hz, the brain no longer recognizes the flicker, and no harmful signals are received.

But manufacturers save money on phones, so the ripple level is usually 200–250 Hz. About 60% of users are susceptible to this level of flicker, so they will experience unpleasant symptoms.

Below are tables with PWM levels in well-known Android smartphones.

Xiaomi phone models Flicker level
Redmi Note 10 Pro 490.2 Hz
Mi 10 Ultra 485.4 Hz
Mi 11 485.4 Hz
Mi 10 Pro 373.1 Hz
Mi 10 362.3 Hz
Black Shark 3 Pro 362 Hz
Redmi K30 Ultra 270.3 Hz
Mi 9 SE 255 Hz
Mi 9 245.1 Hz
Mi 9T 245.1 Hz
Mi 9 Lite 240.4 Hz
Mi Mix 3 240.4 Hz
Mi 8 238 Hz
Black Shark 3227.3 Hz
Mi A3 219 Hz
Poco F2 Pro 177.3 Hz
Mi 8 Explorer Edition 100 Hz
OnePlus phone models Flicker level
OnePlus 8T 458.7 Hz
OnePlus 8 373.1 Hz
OnePlus Nord 367.6 Hz
OnePlus 7T 357 Hz
OnePlus 7T Pro McLaren Edition 294.1 Hz
OnePlus 7T Pro 294 Hz
OnePlus 5 250 Hz
OnePlus 3T 244 Hz
OnePlus 3 243.9 Hz
OnePlus 6T 240 Hz
OnePlus X 237 Hz
OnePlus 6 236 Hz
OnePlus 7 200 Hz
OnePlus 9 Pro 192.3 Hz
OnePlus 7 Pro 122 Hz
Oppo phone models Flicker level
Oppo Find X2 Pro 480.8 Hz
Oppo Find X2 Neo 370.4 Hz
Oppo Find X3 Lite 367.6 Hz
Oppo Reno4 Pro 367.6 Hz
Oppo Find X3 Neo 362.3 Hz
Oppo Find X3 Pro 362.3 Hz
Oppo Reno3 Pro 5G 337.8 Hz
Oppo Reno3 Pro 328.9 Hz
Oppo Reno2 260.4 Hz
Oppo A91 250 Hz
Oppo Reno2 Z 250 Hz
Oppo Find X2 Lite 247.5 Hz
Oppo Find X 227 Hz
Samsung phone models Flicker level
Samsung Galaxy J7 2017 257.7 Hz
Samsung Galaxy Note 8 257.7 Hz
Samsung Galaxy A3 2017 250 Hz
Samsung Galaxy A5 2017 250 Hz
Samsung Galaxy A52 5G 250 Hz
Samsung Galaxy A9 2018 250 Hz
Samsung Galaxy Note10+ 250 Hz
Samsung Galaxy Note20 250 Hz
Samsung Galaxy S10 Lite 250 Hz
Samsung Galaxy S21 Ultra 250 Hz
Samsung Galaxy S8 250 Hz
Samsung Galaxy S8 Plus 250 Hz
Samsung Galaxy Note 20 Ultra 245.1 Hz
Samsung Galaxy A40 245 Hz
Huawei phone models Flicker level
Huawei P40 Pro 367.6 Hz
Huawei P40 Pro 365 Hz
Huawei Mate 10 Pro 247.5 Hz
Huawei Mate 20 Pro 245.1 Hz
Huawei Mate 30 Pro 245.1 Hz
Huawei P40 245 Hz
Huawei Mate 20 X 242.7 Hz
Huawei Mate Xs 242.7 Hz
Huawei P30 240.4 Hz

As you can see, some modern models have a level of light pulses above 300 Hz. But still, most smartphones on the technology market still flicker at a frequency of 200-280 Hz .

DC Dimming - salvation from PWM?

dc dimming

DC Dimming is a relatively new feature pioneered by Xiaomi. The technology allows you to reduce the brightness of the screen, simply by reducing the power of the supplied current. That is, due to a decrease in voltage, the display does not shine so intensely. Flickering still remains, especially at brightness below 40%, but the pulses are no longer so active.

There is also a drawback, and this is color distortion. DC Dimming significantly degrades color reproduction. Colors take on a reddish tint.

color reproduction

The technology is found only in some models. Manufacturers are in no hurry to add it to their smartphones, especially for inexpensive devices. But if you are very sensitive to PWM, be sure to check for DC Dimming before purchasing a new mobile device. So far, this is the only working method to escape the harmful flicker.

How not to feel the influence of PWM

how not to feel PWM

As noted above, some people suffer more from flicker, some less. It is impossible to influence this, but it is quite possible to reduce the influence of PWM. For this:

  1. Purchase smartphones with DC Dimming technology support.
  2. If you feel strong discomfort from flickering, use phones with IPS screens.
  3. Set the screen brightness to maximum. To do this, you need good lighting in the room, otherwise your eyes will hurt.
  4. Activate dark mode not only in the system, but also in all applications that support this option.
  5. Before buying a new phone with an AMOLED screen, pay attention to the level of flicker. Information on the most popular models can be found in the table above.

We found out what PWM is in a smartphone and whether it affects a person. There is no significant harm from flickering, but unpleasant symptoms may appear. Write in the comments if you knew what PWM is and if you experience discomfort from AMOLED matrices.

Author: Алина Никитина Publication date: 20.04.2021

Comments

Total comments: 15
 
 
Александр 0
Почему только Амолед использует ШИМ? В любом телефоне подсветка экрана производиться светодиодами. Там, где не Амолед, матрица сзади подсвечивается, и яркость также регулируется путем ШИМ. Только с другой частотой. Там можно значительно увеличить частоту )))
Так что автор действительно не консультировался с "электронщиками".
18.05.2022 20:20
Reply
N Vladimir 1
Вы бы с электронщиками проконсультировались перед написанием статьи. А то smw какой-то получается...
21.04.2021 22:03
Reply
Zhuravlov Alexei 2
Как оказалось, на меня шим не действует, очень волновался по этому поводу, заказывая Redmi Note 10 Pro, но всё благополучно обошлось, остался доволен своим выбором. А стаья очень хорошая. Так держать!
21.04.2021 17:22
Reply
Клименок Максим 0
В Redmi note 10 pro уровень шима намного ниже чем в самсунгах, хоть и DC dimming не завезли
21.04.2021 19:11
Reply
Land Ber 28
Очень полезная статья, но не без ошибок.
Есть полно подсветок IPS с ВИДИМЫМ ШИМ.
В том числе на ноутбуках или обычных, не flicker frei мониторах.
Надо понимать разницу между пульсацией тока и света.
Если время зажигания/гашения нашей лампы подсветки велико, по сравнению с периодом импульса, то мигать она не будет, происходит сглаживание, как конденсатор в фильтре сглаживает пульсации напряжения. А Светодиоды очень быстрые и мгновенно зажигаются и гаснут, а вот белые "светодиоды" подсветки это синие диоды с каплей люминофора сверху. И медленный люминофор сгладит достаточно высокочастотный ШИМ.
Так мы выходим на крайне важный параметр Глубина Модуляции Светового потока, описывающий амплитуду пульсации и к сожалению полностью проигнорированный в статье.
21.04.2021 08:19
Reply
Колин Максим 4
Прикупил по случаю Asus 7pro. Да, реально, в темноте устают глаза и какое-то муторное состояние от этого OLED. Просто, ужас! Хоть там и есть эта пртивомерцательная опция, но что то от неё не много пользы было. Вернулся опять к старенькому As.max 1 pro Всё таки lPS для глаз лучше, хоть он и не экономичный. Увы, этот ШИМ не для моих глаз:(
20.04.2021 22:16
Reply
Валеев Олег 5
А у Poco F3 какое мерцание?
20.04.2021 22:04
Reply
Kravchuk Olexiy 0
Не согласен на счёт того, что человек видит до 60 гц. Возможно в точке фокуса да.
Но мерцание замечается перефирическим зрением очень хорошо.
Попробуйте посидеть когда монитор сбоку. Сразу чувствуется усталость.
20.04.2021 21:36
Reply
Land Ber 0
Монитор явно не проходит карандашный тест
21.04.2021 08:23
Reply
Арсобов Стас 4
Ну теперь всё понятно!))))а то я думаю что ночью так хренова становится когда долго в смарте сижу!
20.04.2021 21:17
Reply
A Александр 22
а почему в таблице нет таких не менее популярных моделей как Poco F3(к40) или mi 11 lite? они же были на обзорах уже у всех и наверняка многим интересно было бы знать перед покупкой
20.04.2021 20:36
Reply
Лепеншин KRiPo4ek -5
Конечно я итак знал, но я не знал, что в Xiaomi Black Shark 4 вроде как не должен быть заметен шим
20.04.2021 19:48
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PWM on screens in smartphones - what is it, table