How to find monitor flicker rate (pwm) on my laptop?

[peter7277]

Is there a way to find what Pulse-width modulation (pwm) my laptop monitor is using? My laptop is Thinkpad T420.

 

[file3456]

From Google:

Note the width, in seconds or microseconds, of each pulse. This is the pulse width, or PW, of the signal. Calculate the period, or "T", of the frequency, or "f," using the formula: T = 1/f. For example, if the frequency is 20 hz, then T = 1/20, with a result of 0.05 seconds.

So it looks like your laptop can use anywhere from 40 Hz to 60 Hz refresh rate. 40 Hz would be used on battery. The PWM for 40 Hz is: 1/40 = 0.025 seconds and for 60 Hz is: 1/60 = 0.0167 seconds. So you'd have a higher pulse rate at 40 Hz.


Found this article: Sensitive to onscreen flickering? Take caution when purchasing these Lenovo ThinkPad SKUs - NotebookCheck.net News

 

[file3456]

You should be able to adjust the screen refresh rate and even lock it in the display control panel.

 

[peter7277]

I think pwm and refresh rate are different things. Refresh rate can be changed from the display settings, but pwm is hardware built and i am not sure if it can be changed.

 

[iko22]

The CPU fan is PWM controlled. Some case fans are also controlled the same way. You can check your BIOS to see if PWM/analogue conrtol is selectable, but I doubt the option would be available in a laptop BIOS.

Does your problem affect audio, or only display?

 

[file3456]

I think pwm and refresh rate are different things. Refresh rate can be changed from the display settings, but pwm is hardware built and i am not sure if it can be changed.

From my understanding given the equation I gave, PWM is relative to the refresh rate of the monitor in cycles per second in the unit Hertz. By changing the refresh rate in your display settings you will affect the PWM rate as well.

It sounds like these particular laptops have a bad rap for this PWD technique to dim or brighten the screen.

 

[peter7277]

The CPU fan is PWM controlled. Some case fans are also controlled the same way. You can check your BIOS to see if PWM/analogue conrtol is selectable, but I doubt the option would be available in a laptop BIOS.

Does your problem affect audio, or only display?

I have issue with the display. I get eye strain on linux which i have installed on dual boot on the same laptop, and on Windows 7 i don't. I want to find what is the reason for that.

 

[iko22]

Yes, then it looks like a screen refresh rate problem. If your issue is with Linux, there is nothing in Windows that can change Linux settings. The Linux command for adjusting the refresh rate is called xrandr. Higher refresh rates lower screen flicker, it could be that the refresh rate on your Linux is lower than in your Windows. But it could be another compatibility that is causing the problem, for example, if your Linux installation is Updated, or it could be screen resolution, or it could be selection of wrong graphics driver. This Forum isn't really a Linux Forum, so you might stand better chance of resolving the issue, if you post your question on a Linux Forum.

 

[peter7277]

Yes, i know i can adjust refresh rate on linux with xrandr, but refresh rate and resolution on Windows and Linux are the same. I tried everything and i still can't find why on Windows 7 i don't feel eye strain, but on linux i do.