10 days later

I would be careful to say "no PWM". If nowadays manufacturers really use 100 kHz PWM and up, it could very well be that many test setups cannot detect it.
So when reviewers say "direct current is used" or "no PWM is used", just because they see a straight line on their oscilloscope, they might be wrong.

I currently use the BenQ EW2440L, and I can safely say in terms of eye-friendliness it is the best desktop monitor I have looked at so far. That does not mean it is perfect (the uniformity of luminance is certainly not). I have to use it at 0 OSD brightness with reduced contrast, otherwise I would get eye strain and headaches very quickly. With my current settings I can use it for several hours before eye strain and dizzyness kick in, which is a great progress.

I have not found a single LC display (maybe the term "backlight" is more accurate) yet which I can use at higher brightness settings - not even in daylight conditions.

Interesting. I suppose a oscilloscope could be fooled if the PWM was significantly faster then the rate of the oscilloscope.
Ok - so assuming a oscilloscope cannot identify PWM exists - will that cause the same issues? @JTL has a laptop that uses one at high frequency PWM, we'll see how that results over time.

Been up since 4:30 PDT this morning with no direct eyestrain from it (although I got a tension headache due to cold.)

Slacor changed the title to Dell_U2414h monitor .

How do you find the BenQ EW2440L vs other no-PWM LED-backlit monitors? Is it just that it is no-PWM or is there something else about the monitor do you think? Thanks.

Currently I tend to believe all monitors use PWM and that it depends on the frequency if it is detectable or not. I bought the BenQ because it was the very first device that was publicly advertised as being "flicker-free". I recently tried the Dell U2515H, which is supposed to be "flicker-free" (tested, but not advertised), too, and compared it to my BenQ EW2440L.
The Dell almost immediately causes eye strain, although I lowered its brightness and contrast to match the BenQ's low brightness (doing so pretty much destroyed the picture quality).

It's hard to see why there's eye strain:
- Both monitors are supposed to have a true 8 bit panel with (probably) no FRC.
- Both of them were tested to be "flicker-free" (that is, no detectable PWM by using the photo diode + oscilloscope test)

There could be numerous reasons why the Dell, for me, causes eye strain:
- It uses FRC after all
- The PWM frequency is not high enough
- The backlight does not use enough yellow phosphor
- The backlight is too bright at minimum brightness (35 cd/m² vs 19 cd/m²)

I believe it is try and error until we have more information about PWM, the backlight and panels.
What I do not yet understand is why I have to lower the brightness of all my LED devices to a minimum level. In bright sunlight I do not have any problems all day. But looking at an average, much less bright LED screen for some minutes hurts.

I also have an iPad 4 which Is supposed to be flicker-free and which can use at 0 brightness (but not higher). It supposedly has a true 8-bit IPS panel with an A-TW polarizer (the Dell does not have this).
Same goes for my iPhone 4, which is OK at higher brightness settings if I do not use it too much during the day but I had to buy and test several iPhone 4 and 4s just to find a device with a usable screen. Not sure if the reason is different display charges or the OS version. The iPhone 4 I got is still on iOS 6.0.1. All other device were either on iOS 6.1.3 or even iOS 7.

  • oxlr replied to this.

    Wow thank you for that very detailed response.

    I have the same problem with inside vs outside. Inside my pupils are enormous (even while viewing a bright screen), taking up most of my iris. I notice that my pupils are much bigger than other peoples inside. Outside, even if it is overcast and not that bright will shrink to a pinprick, just like other peoples. That enormous difference in pupil size must let much less of the device brightness in, even if the device is at max brightness. Also the ratio of sunlight vs LED light will be massively changed, so that only a fraction of the light entering you eye is from the LED device, rather than mostly from the device. This could be very important if there is a neurological component involved in the eyestrain.

    I know that certain wavelengths of light are necessary to trigger pupil constriction. Maybe as a % of light coming from an LED-backlit device it is not enough to trigger the necessary constriction.

    It could also be that reducing brightness becomes somewhat of a zero-sum game up to a point (say 25-100& of brightness, up until the pupil will expand no further with further brightness reduction). Reducing the brightness will just cause the pupil to dilate letting a similar amount of light in. This makes ambient lighting super important. I used to shine a "full-spectrum" CFL task lamp into my face as I viewed my monitor. I then put the monitor on low brightness. Result: pupils constricted with a low monitor brightness.

    Crizal prevencia is unique in computer oriented coatings in that it is supposed to block the harshest of blue light but leave the pupil constricting wavelengths to get through. I havent tried it though.

    Edit: I have just purchased the BenQ monitor. I'm excited!

    Do you need to have your monitor hooked up to an Nvidia GPU for eyestrain purposes like some do? I'm hoping to try the BenQ with my Windows laptop, but unfortunately it only has Intel GPU.

      degen I had to replace my AMD card with an Nvidia card to get rid of AMD's forced temporal dithering. At first I thought the monitor was not that eye-friendly, but after I had replaced the AMD card the difference was like night and day.
      BTW: The power supply unit has a green LED which flickers, probably at wall power frequency.
      If such low frequencies affect you, too, I suggest covering it with some tape.
      In fact I have all my LEDs on all my devices (even the monitor) covered with black isolating tape, which I agree is an extreme measure but it helps to narrow down the sources of eye strain.

        The new BenQ monitor, EW2440L.. I am trying to keep my elation under control

        Received it yesterday (God bless Amazon, hehe). Still early, but this is the second day and with huge reservations.. This is the best monitor I have used since this whole fiasco started.

        BenQ is releasing a an upgrade to the 24 and 27 inch EW series monitors that will feature "Low Blue Light Plus". I'm not holding my breath, but it sounds promising.

        If this works out.. This whole issue has kept me out of school..

          degen If this works out.. This whole issue has kept me out of school..

          Do you think you can start a new thread with how it goes? 😃

          • JTL likes this.
            14 days later

            degen Could you give a review of the BenQ monitor?

              I will give a review of the BenQ monitor soon. This is my first day back on the computer since I strained my eye heavily using the BenQ, so I want to take it easy.

              I was so elated that I could use a monitor again that I was on the computer for 6-8 hours the first day I used it and I ended up with terrible eyestrain. I suspect that with even a good monitor my eyes will not be as resilient as they were before this whole fiasco started.

              Because my eyes have been weakened from years of eyestrain, even reading from paper gives me eyestrain and it's not fair for me to judge this monitor without using it for several days consecutively without binging.

              It's hard for me not to be skeptical at such an improvement, but so far this monitor seems to be only a little worse than reading from paper, which would make it an enormous improvement over my previous PWM-free monitor, the HP ZR2740w.

              Hey degen, are you using the monitor in a known "safe" environment, for example Windows + NVIDIA? I am saying this beause just recently I tried various Linux distributions for many hours and got strong eye strain, too. But it was not the monitor, it was Linux. What are your OS and your graphics card?

              I am using Windows 8.1 with an Nvidia GTX 650. Still so far the BenQ a good improvement over my HP ZR2740w and arguably my old CCFL-backlit LCD as well.

              The temporal dithering "snow" effect is very apparent to me on my laptop with an iGPU but it is definitely not there on my desktop setup.

              Hmm... I do not think you should give up yet. What did you do during those hours? In my opinion Windows itself is safe (I skipped Windows 8 though), Firefox is safe, some games are definitely not, watching videos may be difficult, too. The last Chrome I tried a few months ago: not safe. So even when the hardware is set up in the right way, certain desktop programs and mobile apps may cause eye strain.

              dev