How to test my Monitor for PWM flicker?

and What to do about it

There are several devices which you use the test your monitor for PWM flicker but I want to show you something simpler.

The test below is based on a simple moving line on your screen.

You need to test your monitor at MAX hardware brightness and at MIN hardware brightness.

By hardware brightness, I mean to change the brightness from your monitor or laptop buttons.

PWM flicker test

Below you can see a white line moving really fast.


You can open this in your own browser TestUFO Blur Trail test.

We will use this to determine if your monitor has PWM flicker or no at both max and min brightness.

I will tell you what to look for but first a little intro on

What is PWM flicker?


PWM flicker is a cheap way that manufacturers use to control the brightness of the screen by adding some breaks without light.

Basically, on a given interval your monitor is OFF then after some milliseconds ON again.

Our brain is slow and we don’t perceive this but we get huge eye strain and eye pain from this.

This is one of the main reasons why our eyes hurt in front of the computer.

Because of this constant ON and OFF of the backlight our eyes contract all the time like this

This is why PWM flicker causes so much eye strain and is undesirable.

Most monitors flicker only when the brightness is lowered so when the hardware brightness is at 100% there is no flicker.

This is why my recommendation when you download Iris is to set your hardware brightness to the MAX and control the brightness with Iris.

Iris uses another method to control the brightness which doesn’t cause eye strain and eye pain.

What to look for?

Depending on how you see the moving line you can determine if your monitor uses PWM to control the brightness.

If your monitor doesn’t use PWM you will see a smooth moving line like this

You can test this by setting your hardware brightness to 100%.

When your hardware brightness is set to 100% your monitor doesn’t use PWM in all cases and you should see this smooth line.

Now set your hardware brightness to the minimum possible value.

If your monitor uses DC dimming instead of PWM the test line should look smooth like this

If your monitor uses PWM to control the brightness you will see multiple lines on the screen separated by some space like this

What to do if my monitor uses PWM?

1. Set your monitor Hardware brightness to 100% using your monitor buttons.

2. Use Iris to control the brightness without PWM

Tell Friends

If you liked this article and you learned new things about why we feel eye pain in front of the monitors

If you want more and more people to learn about this

If you want your friends to protect themselves from the monitor harmful rays and emissions

32 thoughts on “How to test my Monitor for PWM flicker?

  1. I’m using IRIS full version since last December, and do far I can tell the difference from before. Mostly my eyes can tell ? Less eyes strain for sure and more concentration on things I work on. Thank you!

    1. Thanks for supporting us and for being our customer, Patrizia 🙂

      Very happy to hear that Iris has made a difference in your life, that’s why we are here

    1. Here’s what I would recommend:
      1) Remove PWM Flicker:

      2) Pick a low enough blue light value that’s also comfortable with you
      You can try Sleep type which has 0% blue light but it’s really red and might be a tad hard to look at your screen
      If it’s not comfortable for you, you can try a higher value

      You can manually change blue light values like this:

    1. Iris Pro is the full version of Iris that has all the advanced settings and features like more advanced timer settings, brightness, blue light, monitor manager, color schemes, font manager and much more.
      You can find it here:

      Iris mini is a minimalistic version of Iris, it contains only the most basic features that will protect your eyes. You can get it here:

  2. I am not sure to understand where is the test. Is it the UFO test with just a line moving, or is it something with that text? Because I do not find anywhere that test with the text…
    About the UFO with lines, the line, even at max brightness, doesnt appear to me as a totally clean line. Which means, it either flickers at max brightness, or it doesnt and I see multiple lines because of something different (no, no LSD).
    I have tried to slow down the line and it became a clean line and it is a clean line also at min brightness.
    So I am confused. Does my display I have PWM?
    According to Notebookcheck this display has PWM at 200hz. I would like to have a more effective testing method.
    You could include one in the app…

  3. Привет из Москвы! Спасибо за ваш труд!
    Now working experience is much better without that flicker but there’s still some weird color blinking being noticed via phone camera… Do you know if that’s ok?

    1. There are some very rare cases, depending on your monitor, that Iris will not remove absolutely all of the flicker, it also depends on the settings of Iris that you have, so it’s possible

      1. After some research I found that it is moire pattern effect caused by something like difference between monitor pixels and particular camera pixel scanning system. Sorry for inaccuracy describing the issue. I do believe that there’s no such effect if you are not filming the screen. Am I correct?

  4. This makes no sense. Both on max brightness and minimum I see the single lines moving. Nothing changes.

    Additionally, the software does not dim my computer when on automatic and health. I think there’s a bug in the software and I am also confused on the above!

  5. My old desktop monitor just died. We need to get another one and set it up with Iris. Can you tell me which monitor you would buy if you had to get a new one? We want to get the best possible one for eyes and then add Iris to make it perfect.

    Also, are curved or flat screen monitors better for the eyes?

    Thank you!

    (We’re in the U.S., if that makes a difference re: availability.)

  6. I could not follow at all what you were trying to teach. am I to view all these lines as they appear now on my computer? Are you trying to sell me some program or just help me know how bad or good my computer is for my eyes?

    1. Hi Theresa,
      You can follow the explanations on the page as to how you’re supposed to view the lines and whether or not your monitor has PWM flicker
      What you use this test for is completely to your choice 🙂

  7. Hello,

    I think there might be something wrong with this test page.
    It says “Bellow you can see a white line moving really fast.”. But I can’t see any moving white line at all. I can only see the example still images under “What to look for?”.
    There is, however, a seemingly miss-placed text reading “PWM test” far to the left of the text reading “We will use this to determine if your monitor has PWM flicker….”. I’m guessing the test is meant to show up here?
    Tried 3 different browsers. All show the same. No moving images except the eye GIF.

  8. How do you set the brightness on the hardware ? Where is this tool located? Please advise. Thank you in advance. Patricia

    1. Hi Patricia,
      To set the brightness on your monitor you need to look for the button on the monitor itself

  9. Where did the GIF versions go? Is it possible to get them back as alternatives to the Youtube video, please? The video display seems to have some problems on my computer, it’s hard to clearly see if it flickers or not. I remember viewing this page earlier when it had the GIF versions, and they were displayed fine.

  10. I agree with TJ and others, about the needless confusion engendered by this piece, and you have failed to address any of those comments. To be precise: this article lacks clarity. In particular, after your text “If your monitor doesn’t use PWM you will see a smooth moving line like this” you have a picture of a thick white bar that blurs into blackness. Which I don’t think represents a moving line at all and is not something that I see. There is no test for the text images displayed either. So why are they even there? Please review.

    1. Completely same.. I am an Engineer and programmer ,and after 10 min. on the page I was suspicious about myself , if I am an idiot not to find a TEST ??.. Good to know I am not alone.. There is no “TEXT TEST” on the page to compare this
      results : ??

      Forget about “Testing 123” text , I am just looking for the moving line (first iframe not the yt videos) and again comparing it with the lines in the :
      Result : Again None of the patterns , look like my pattern , I see 2 ghost lines moving with my original line with 1,5 -0,8 mm offsets (left and right of the original respectively)..
      So what ?

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