Wednesday, December 26, 2012

Monitors with no PWM

The vast majority of monitors today use PWM (Pulse width modulation) for dimming the backlight. To make things even worse the frequencies at which the backlight is being cycled on and off are quite low - somewhere between 180Hz and 240Hz, which makes it very likely for the flicker to be perceived by humans. As a result various health issues might occur - eyestrain, headaches, dizziness, etc. If you're suffering of any of this, you might want to consider getting a monitor which does not use PWM such as:
  • Dell S2740L
Beware that its coating is a glossy one, making it a highly reflective if used in bright environments. This can cancel any benefits of it being flicker free unless you can use it in a darkened room. Since it's a 27-inch screen and it only has a resolution of 1920 x 1080, it's susceptible to the screen door effect. On the positive side, the text size is bigger out of the box, so that can save you the trouble of adjusting the font sizes in different programs. It also has very low input lag which makes it suitable for gaming.

  • Dell U2713HM
While this one is also in the 27-inch class, it's quite different from the monitor above. First, it has a light AG coating and a resolution of 2560 x 1440. Unfortunately, it has some downsides especially if you're looking for a monitor for color critical work as it covers only about 72% of the Adobe RGB space. Having said that, I really like the fact that there is no FRC used, which means there will be no color flickering. Correct me if I'm wrong, but I believe that would make it the only monitor that is indeed flicker-free as all the rest of the screens in this list incorporate frame rate control.

  • Dell U2713H
Although this screen is quite similar to the HM variant we've already seen but it should be said that it's a lot more suited for design work as it offers support for hardware calibration and it has 97% coverage of the Adobe RGB. The one thing I'm concerned about is the use of Frame Rate Control in order to simulate the 1.07 billion colors because its panel is natively only 8-bit. The reason I'm mentioning this because there is a chance of color flickering, which can undermine the benefit of the absence of PWM.

  • HP ZR2740w
The problem is that there are two revisions of this monitor available with some significant differences between them. The original version didn't have an on-screen display menu and had a quite aggressive anti-glare coating. The newer ones provide remedy for these issues but I don't think there is a way to tell which one you will get.

  • ViewSonic VP2770-LED
Here is yet another 27-inch 1440p display that has a PLS panel. The good news is that it has a light AG coating. But I find the usage of FRC worrisome because it can lead to color flickering meaning despite the lack of PWM, we can't declare this screen to be truly flicker-free.

Another one I'm personally looking very much forward to is BenQ GW2760HS which will be the only monitor with VA panel and no PWM! (as specified by the manufacturer.)

18 comments:

  1. You forgot Samsung S24A850DW - a smaller model using the same PLS matrix

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    1. It appears that the 27-inch model (S27A850D) is using PWM at low brightness levels, so can you confirm whether that is also the case with the 24-inch version, or it's completely PWM-free?

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    2. I tested S24A850DW using TFTcentral method with my DSLR, and it uses PWM.... The unit was made in Mexico this February.

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  2. And what about EIZO EV2736W-FS 27" IPS, 2560 x 1440, sRGB color, same specs except 1440p. I'm personally interested of two brands: EIZO and NEC. Sorry for the others!

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    1. I've added it to the Hybrid Dimming section.

      I wish there was a screen with a VA panel in the EIZO EcoView series, because apart from the IPS and PLS monitors, they even have two "flicker-free" with TN panel: EIZO FlexScan EV2416W and EIZO FlexScan EV2316W.

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  3. Could you review some laptop screens (Samsung Series 9, Macbook Macbook Air, etc.)?

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  4. According to Extrahardware.cz review and measurements Samsung S27B970D uses combination of voltage regulation and PWM at 182 Hz.

    Briefly translated:
    “As well as S27A850D , S27B970D also uses quite remarkable combination of lowering voltage and PWM brightness control. Roughly up to 140 cd/m2 is regulated without PWM at lower levels then with PWM, and the frequency is less than 182 Hz. That was not much, if it were only regulated by PWM. When the combined brightness control such frequency would you not mind, perhaps the most sensitive of you maybe.”

    Source:
    http://extrahardware.cnews.cz/samsung-zpatky-elite-s27b970d-je-stylovy-27-pls-hw-kalibraci/strana/0/10

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    Replies
    1. Thank you for pointing that out!

      I have updated the article to reflect your remarks.

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  5. Is there a laptop that has a screen that does not use pwm? A smartphone? At the moment all new led laptops (MBP and Sony)that i owned gave me severe eye strain. The same with samsung galaxy 3 and iphone 4s.

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    1. Apologies for replying so late.

      Have you tried using CCFL-backlit laptop since this type of backlight can (to a certain degree) mitigate the effects of the PWM? Unfortunately, these are hard to find as they are not being manufactured anymore. Also, there is no guarantee that the CCFL backlight will actually help you so I'm not sure whether this path is worth pursuing.
      In case of using a LED-backlit laptop, have you tried setting the brightness to 100% since in most cases the PWM is not used at that level (provided that it doesn't become too bright for you to use).
      I think most (if not all) of the battery-powered devices are employing PWM since it's more economical on the battery. That's not necessarily to say there aren't some laptops that are PWM-free but there are too many conflicting reports out there so I don't want to mislead you by giving you wrong information.
      There is possibly a quite helpful discussion (over 60 pages) at the Apple forums regarding PWM/eyestrain. Products from other brands (including smartphones and laptops) are being discussed as well:
      https://discussions.apple.com/thread/1677617?start=900&tstart=0

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  6. Do you think the Dell S2240L is PWM free?
    Or is it only the 27" version that's free of it?

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    Replies
    1. I'm sorry for taking so long to reply.

      According to Dell support, S2240L is using PWM:
      http://en.community.dell.com/support-forums/peripherals/f/3529/t/19484238.aspx

      If you're looking for a 21.5" IPS monitor, you might want to check out Acer H226HQL as it's completely PWM-free according to this review:
      http://extrahardware.cnews.cz/recenze/acer-h226hql-barevne-verny-jemny-levny-leskly-ips-bez-pwm-test/strana/0/10

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  7. Great webpage, very helpful. Darn PWM

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  8. Thanks for your great work. Do you know the Dell U2412M is PWM free?
    Thanks again.

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    1. I don't know for sure but there are some reports that suggest it's using PWM, unfortunately. That being said, the latest revision of this monitor is supposedly using considerably higher PWM frequency (>1000Hz), but it's still not PWM free.

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  9. great review! thanks a lot! Any idea when the BenQ GW2760HS will be available in Canada? Couldn't find anything about this on the web...

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  10. Dell 2312HM is PWM Flicker free

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