Most current cell phones come with an OLED screen, a technology that flickers the screen to generate the illusion of low brightness, which is known as PWM or pulse width modulation. When this flickering or flashing of the screen is not fast enough, it can cause visual fatigue and even headaches and even nausea..
How brightness control works on cell phones
Very basically, OLED screens are a set of tiny diodes or "bulbs" that turn on and off individually to display what appears on the screen. That is, they cannot be turned on halfway, which is why an electronic technique called PWM is used to control the brightness of the screen. It consists of turning the LED diodes on and off many times per second, to generate the illusion to the human eye that the screen is more or less bright, depending on the duration of these on-off cycles.
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How much PWM should a cell phone have?
When the PWM of a cell phone screen is low, 240Hz or less according to Android Central, the user may experience visual fatigue, headaches, and even nausea. This can become so unbearable as the days go by that you won't even be able to use the phone for less than a minute without feeling discomfort. The minimum PWM mentioned may need to be doubled for people with eyes more sensitive to screen flicker..
Where do I see the PWM of my cell phone?
Unfortunately, PWM is not an obvious technical specification. It can be omitted by the manufacturer itself and it will be necessary to do a little research on the Internet to find it. There are very technical websites like notebookcheck.net , where they measure this parameter. For example, that's where I found out that my Samsung Galaxy A52 has a PWM that doesn't even reach 200Hz.
Nicholas Sutrich's reviews on Android Central should also have this parameter. This author mentions that Motorola phones are the best in this regard. For example, the Motorola Edge 30 series, Razr 2022 or the ThinkPhone all have PWM above 700 Hz, so they are phones that should not cause vision problems or discomfort to anyone..
There are phones as premium and expensive as the iPhone 14 Pro Max or Samsung Galaxy S23 Ultra that only have a 240 Hz PWM. Other cell phones like the Galaxy Z Flip 4 come with a negligible 120 Hz PWM.
PWM vs refresh rate
Do not confuse PWM with the refresh rate of a screen. My Samsung A52 phone mentioned has a refresh rate of 90Hz, which means that the image on the screen is updated 90 times per second, and it is something that is noticeable when there is a moving image, for example when scrolling. This parameter, the higher the better, because it certainly benefits the eyes and the eyes get less tired, but it has nothing to do with the 200Hz PWM that this device has, which as I said refers to the control of the lighting or brightness of the screen.
LCD screens with PWM?
It is assumed that this only affects screens with OLED technology and that LCD screens do not have this problem, because in this LCD technology the screens are illuminated by a backlight, whose intensity could be regulated. These should be flicker-free screens, however, this is not entirely true. There are LCD screens that make use of PWM to reduce the brightness of the backlight in this screen technology. That is the case of TCL TVs with LCD screens, whose PWM is just 120Hz.
Conclusion
Unfortunately, cell phone manufacturers use a low PWM in OLED screens because this helps to extend the useful life of this screen, specifically to prevent the screen from burning. But this can also affect the eyesight, not only of people with the most sensitive eyes, but in general of any person, since exposing your eyes to a light source that is constantly turning on and off cannot be a good thing for the eyes. view.
Source : Android Central