Perhaps you’ve noticed that the Laptop Media team has started testing every laptop for pulse-width modulation. PWM is used to regulate the brightness of LCD and LED displays. How does that concern us?
The pulsations can be bad for your health and more specifically for the users’ eyesight. They can lead to migraines, headaches or other forms of discomfort after long-term usage. In most cases, those pulsations have a frequency somewhere around 200Hz. They cause multiple contractions and expansions of the pupils, which bears down negatively on your health. They are especially harmful in models with LED backlight because the colors of the emitted light are not as inert as the colors of the CCFL backlight and so they reach high amplitudes and rapid luminance changes.
Basically, the problem comes from the flickering light, not from the crystals of the LCD monitors.
>> Top Laptop PWM Ranking (Rated by negative impact on eyesight) <<
Pulse Width Modulation (PWM) is an easy way to control monitor brightness. When you lower the brightness, the light intensity of the backlight is not lowered, but instead turned off and on by the electronics with a frequency indistinguishable by the human eye. In these light impulses, the light/no-light time ratio varies, while brightness remains unchanged, which is harmful to your eyes. If there is PWM, it is better to have a high frequency of around 20000 times per second instead of, say, 200. This is noticeable at different brightness reduction levels for different monitors. It is noticeable to a higher degree in LED than in CCFL backlights due to the former’s lower afterglow and higher nominal diode brightness.
Here are the waveforms of 4 displays. The first one doesn’t emit pulse-width modulation, which provides the option to work for extended periods of time. The second is a classic PWM. Its aggressive pulsations at a low frequency put extra pressure on the eyes and brain. The third also emits PWM, but it has an extremely high frequency, which is considered to be less harmful. The fourth one doesn’t flicker unless the brightness is <25%, so it is eye-friendly in practically every normal usage mode.
So if i replace the screen, will i still have PWM on my screen? i mean, which part of the laptop use PWM. The screen or the laptop?
Current laptop screens are typically using an eDP connector for the “embedded display port”. The specification is a secret only available for manufacturers. I have seen some datasheets for screens and they show the eDP connector has the PWM signals coming from the laptop to the screen. I think the PWM is the primary way a computer tells the display how to set the backlight brightness if I understand the datasheets correctly. The display datasheets tell the computer manufacturer the frequency range needed and the computer firmware tells the computer how to generate the PWM. Any replacement screen would need… Read more »
Same question, what can we do? How can we know about the technology of new LCD laptop screen, is it flickering or not before we buy? If I replace LCD screen does it help? Can we replace just back light panel?
Hi! To detect PWM unused my phone’s camera with a camera app that lets you play with the shutter speed. You set the shutter speed to the fastest and you can see if the screen flickers. No need to take picutes.
Hope it will help people suffering from pen.
[…] Pulse-width modulation (PWM) is an easy way to control monitor brightness. When you lower the brightness, the light intensity of the backlight is not lowered, but instead turned off and on by the electronics with a frequency indistinguishable to the human eye. In these light impulses, the light/no-light time ratio varies, while brightness remains unchanged, which is harmful to your eyes. You can read more about that in our dedicated article on PWM. […]
[…] Pulse-width modulation (PWM) is an easy way to control monitor brightness. When you lower the brightness, the light intensity of the backlight is not lowered, but instead turned off and on by the electronics with a frequency indistinguishable to the human eye. In these light impulses, the light/no-light time ratio varies, while brightness remains unchanged, which is harmful to your eyes. You can read more about that in our dedicated article on PWM. […]
[…] Pulse-width modulation (PWM) is an easy way to control monitor brightness. When you lower the brightness, the light intensity of the backlight is not lowered, but instead turned off and on by the electronics with a frequency indistinguishable to the human eye. In these light impulses, the light/no-light time ratio varies, while brightness remains unchanged, which is harmful to your eyes. You can read more about that in our dedicated article on PWM. […]
[…] Pulse-width modulation (PWM) is an easy way to control monitor brightness. When you lower the brightness, the light intensity of the backlight is not lowered, but instead turned off and on by the electronics with a frequency indistinguishable to the human eye. In these light impulses, the light/no-light time ratio varies, while brightness remains unchanged, which is harmful to your eyes. You can read more about that in our dedicated article on PWM. […]