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  • CoreLinker Level 1 Level 1 (0 points)

    mojar, I am really surprised your Samsung s27b970d flickers. Prad is a German site, so I guess models from different regions or maybe even different series use different dimming methods. I would not question their (Prad's) methods.


    You should try the Dell u2713hm. I can confirm it is flickerless, though I'm in Europe. But I think review sites from all over the world have confirmed it's PWM free.

  • Eric Leung1 Level 1 Level 1 (5 points)

    I guess I have raised a controversial topic in my previous post

    Please allow me to elaborate more on my thoughts on the eye strain issue.


    Let's begin with some assumptions:


    First and foremost, we agree that a lot of the displays (both from Apple and other manufacturers) in recent years are giving serious eyestrains to us with sensitive eyes that we didn't experience previously. Since the displays in question appears to be mostly LED backlit, we believe the problem is highly related to LED.


    Secondly, the problem cannot be solved by simply adjusting the brightness. It is also un-related to glossy screen, reflections nor glare. These issues are simple to fix by pressing the F1 key on the Mac keyboard or re-orientate the computer / mobile phone. As some others have mentioned, we have been there, done that. But those didn't help with our problem.


    Thirdly, majority of the population doesn't seem to be affected.




    Now, from what have been discussed in this forum and from what I have experienced, I believe there are multiple causes for the eye strain. I think we have sort of identified three main causes of eye strains from the displays, briefly described as below:


    Type 1


    PWM (Pulse-width modulation), a way of flickering the backlight in order to control brightness. The identification of this issue is what started this thread years back. For some time, we believed this is the sole reason for causing the troubles. However, recent tests have shown that all recent Apple products are PWM free. Be it iMac, MacBook Air, MacBook Pro, iPhone or iPad, they all exhibits constant backlight at various level of brightness. No trace of PWM at all. So, if one is having eye strain issue with an Apple product, it's unlikely due to PWM.

    Many displays from other brands, however, are likely still using PWM for dimming and thus would flicker when they are not at full brightness. (and some would flicker even at full brightness)



    Type 2


    A mysterious and hard to detect flicker. We think the screen is flickering in some way, but we are not exactly sure how. Somehow, it seems this kind of flickering makes our eyes work harder than usual to focus when reading on the screen. After some time of viewing, our eyes would get exhausted and thus getting sore eyes, headaches, etc.


    It seems the symptom is more apparent when trying to read texts and is much more accommodating when viewing graphics or movies. Perhpas because there's less need for our eyes to resolve the edges of a photo or motion picture clearly (we usually interpret the entire photo or the series of motion pictures as a whole).


    Some believes this is due to the dot-inversion process of the LCD display. This is due to hardware design and calibration, and is easily detectable with tests like those exhibits in 's LCD tests.

    These tests, however, doesn't seem to show very high consistency as to identify which display is comfortable and which is not.


    Another thought on this mysterious flicker is that there is some sort of random flickering at the subpixel level, and could be software / driver related. Since some has experienced eye strain after upgrading the OS on a Windows PC, and some reports mentioned a similar eye strain happens in a CCFL monitor as well.


    Anyhow, for some displays, it seems changing the monitor resolution to a lower and non-native resolution appears to ease the discomfort. It is not exactly sure why. Though we think it might be because the subpixel flickering signals have been corrupted at the non-native resolution screen.



    Type 3


    The backlight itself is causing a form of migraine directly, not through flicker. This hasn't been well discussed previously. Mainly, I got aware of this issue throughout the two months when I tried to identify and to solve my problem with the iPhone 5, and I detailed what I thought about this particular issue in my previous post.


    One of the main reasons why I think the light is causing the problem itself and isn't related to other issues is because I get the same uncomfortable feeling as looking as the screen when I light up a dark room with the phone's flash light. (and no, I'm not looking at the strong light source!)


    Reducing the brightness on the phone surely helps, but doesn't eliminate the problem.


    I am suspecting this has a relation to the strong blue intensity of the LED backlight. The main reason I say that is because the discomfort symptom appears to be largely reduced / alternated when I filter out the blue light with the rosy red coated glasses.


    My best *guess* for why is that causing trouble is that human eyes are more sensitive to green rather than blue. When my eyes are looking at the "white" display, due to the sharp difference between blue and green intensity for LED (blue intensity is much higher than green), my eyes don't pick up the brightness correctly. They probably are more inclined to picked up green rather than blue as an indicator of brightness and the pupils don't contract enough, and thus allowing more than appropriate amount of blue light hitting the retina. And my sensitive eyes don't like it.


    However, I could be wrong about this blue intensity assumption. As Topher has mentioned, the light intensity coming out from the LED backlight should be weak compared with other light source such as sunlight or light bulb (which we found comfortable). I also couldn't fully eliminate the discomfort when I tried filtering out the light.

    So, it could be something else other than the blue in the light spectrum. Though, I'm pretty sure there're some problem with the light itself.


    Also, this issue only appears in some particular type of LEDs, and I'm very sure that not all LED lights are causing this same trouble. For example, all my pre-iPhone 5 iPhones, iPad 1 & 2 and my old LED iMac don't have this problem. However, the iPhone 5 is especially bad in this regard, and also the iPad mini (but the iPad mini is much less severe than the iPhone 5).


    Of course, please understand that I'm no expert in lights, and I can only use eyes as light detectors. What I'm talking is only my best guess. I honestly hope I could have some proper equipments to help analyze and support my guesses in a scientific way.





    So, when we are feeling troubled looking at the screens, it could be one of the three types of causes mentioned above, or it could be a mix of two or three. Also, some people could be more sensitive to a particular type than others.

    I, unfortunately, seems to have troubles with all three types...

  • mvanier Level 1 Level 1 (0 points)

    Eric, thanks for the review of the most common theories for monitor eyestrain!  I've been arguing for your type 3 explanation, as I'm pretty sure that it's the LED light itself and not e.g. PWM that is causing my particular problems (though of course if the LED light is already problematic, adding PWM may aggravate it). 


    Let's think about what white LEDs (wLEDs) actually are.  They are really blue LEDs with a yellow phosphor, so their spectrum has a big and fairly sharp blue peak and a more diffuse yellow peak.  The eye perceives this as white, but the eye also perceives sunlight (with a much broader spectrum) as white, and fluorescent light (also a broad spectrum, but somewhat shifted towards blue with some spikiness) as white.  So the fact that a backlight appears "white" is very deceptive.  If the "white" is largely blue, even when you turn down the intensity to what appears to be a low level, there is still plenty of blue.  Worse, since the irises in your eye respond to overall intensity and not the intensity of any particular color, they dilate to let in more light at low intensity (of course, this will also depend a lot on ambient light conditions).  So even though the _overall_ light may be rather low, there could still be too much blue for comfort. 


    I first noticed problems with blue light long before I had problems with LED backlit monitors.  There is (was?) a kind of incandescent light bulb called "Reveal" by GE that is just a regular light bulb coated with some kind of neodymium compound to shift the light spectrum to the blue end.  It's supposed to look more like sunlight.  Well, sunlight or not, I couldn't use it for more than a few minutes; it gave me _horrible_ eyestrain.  I've later read that blue light is very difficult for us to focus on because our fovea (center of the retina) contains predominantly retinal photoreceptor cells that respond to red and green, which is what we mainly use for high-acuity vision.  When there is mostly blue, it's hard to focus on e.g. text, and our eyes can go into a focus/defocus loop which causes severe eyestrain.  This sounded like an interesting theory, so I tried using the f.lux program on my mac (with a CCFL monitor this time); lowering the blue light (the "color temperature") caused a very immediate drop in eyestrain!  Before this, I was convinced that PWM was the source of my eyestrain problems; now, I'm pretty sure it's the color spectrum of the LEDs. 


    I'd love it if the industry would create better white LEDs, but I'm not holding my breath and I certainly don't expect Apple to fix this problem (they could care less about a problem that only affects 5% of customers).  I encourage people with eyestrain to use external CCFL monitors (while you can still get them!).  A new CCFL-backlit monitor should last at least five years, after which there will hopefully be better alternatives.

  • Topher Kessler Level 6 Level 6 (9,790 points)

    You can adjust spectral imbalances by applying a different color profile to bias the output to another part of the spectrum. You can adjust this when calibrating your display by adjusting the color temperature. You can also use other display calibration tools to shift colors in other ways, far beyond what's possible with Apple's provided utilities.

  • mvanier Level 1 Level 1 (0 points)

    That's exactly what f.lux does, as I alluded to above.  See  Unfortunately you can't use it with a non-jailbroken iPhone, and as far as I know iOS 6 hasn't been jailbroken yet.

  • Eric Leung1 Level 1 Level 1 (5 points)

    Thanks Mvanier


    And thanks for your comment on the Reveal light bulbs too! I have thought of buying the GE Reveal bulbs in replacing some of my fluorescent lights, I guess I can abandon that idea now, haha.



    By the way, I came across a linear polarizer today. Out of curiosity, I briefly looked through it to see the screen of an iPad mini, and it appears to be able to cut down the eye strain!


    It could be just because the brightness has been lowered due to my polarizer, though, I have also tried nake looking at the iPad mini with the backlight reduced by half and it didn't seem to achieve the same level of clarity and comfort.


    I'm now wondering perhaps the arrangement of the polarizers inside the LCD screens has a relation to our eye strain??


    The time that I spent with that was brief so I'm not very certain, need to do more tests later to confirm.

  • mojarvinen Level 1 Level 1 (0 points)

    The polarizer could be one thing. Since I yesterday tested with a DSLR my new Dell e6430 and confirmed, that it does not have the flicker, but it still is not good for my eyes. Though, this could be that my eyes are now just so strained from using weeks the Dell U2412M.


    But my previous Samsung 275T had an interesting polarizer - everything near the screen (like the keyboard, my hands etc.) looked like I was using polarized sunglasses. As I understand, all LCD screens have a polarizer, otherwise one could not see the image at all. So yes, the polarizer type could be one thing that affects the eye straing. The 275T did not cause eye strain.

  • rohanzsta Level 1 Level 1 (0 points)

    I'm in the same boat as everyone who posted here and I can no longer use Macbooks at all.


    I have a side question though: For people who cannot look at newer Macbook screens, are you guys comfortable using an iPhone 4/4s/5 ?


    My cell phone contract is ending and I need a new phone.. I'm wondering if this problem translates over to the iPhone?

  • Gurm42 Level 1 Level 1 (0 points)



    Sadly there is no simple answer on that. Some of us have no problem with iPhone 4s (my own phone and my wife's are both 4s's and I have no issues with it). Some do... since some folks are still very sensitive to Retina displays! The only way to tell is to try one for a half hour at your local store.


    Sorry there isn't a more definitive answer!


    - Gurm

  • LovesDogs0415 Level 1 Level 1 (0 points)

    I can tell you that I am unable to use the newer i Touch.  I believe that the problem translates, but I don't understand the differences between the 4/4S/5, even within the version.  I did not notice the problem looking the screen of the iTouch in the store over the days and times that I was deciding to buy.  However, when I got it home and tried to use it, it was clear that the problem was there for me.

  • Gurm42 Level 1 Level 1 (0 points)



    Wanted to share that I have updates on my particular situation.


    I've determined several things.


    First, I've figure out that my current eyestrain is stemming from the fluorescent lights in my particular area at work. I'm wearing a visor and using a monitor hood to lessen the eyestrain, and taking frequent breaks and walks outside of my area.


    Second, I've found that the retina MBP isn't bothering me anywhere near as much as it did previously. Maybe the strain it is causing is being lost in the background noise of the generalized eyestrain from the lights, but I find I can use it for moderate activity now without any "additional" discomfort. I haven't really tried using it for an hour of solid websurfing.


    Third, JEEZ the retina display is gorgeous. I'm actually actively sad that it has been causing me problems, because it is quite literally the crispest, best display I have ever seen.


    Fourth, I have done some outside reading and found that many things can cause issues in this regard. Stress/anxiety (which I have) can increase sensitivity (there are several medical papers which find that photosensitivity - especially to fluorescents and flicker - goes up with stress/anxiety levels). Physical fitness can be an issue, and eye health in general. So I'm going to get religious about taking walks, lowering stress, and taking my vitamins. Luckily for me we are moving in a couple months to a new location which will have much better lighting. I can't wait!

  • Eric Leung1 Level 1 Level 1 (5 points)

    Gurm42, do you have a polarized sunglass? Can you see if it helps make you relieve the eye strain with the Retina MBP? (note that it may make your screen goes black, and you may need to rotate your head or the screen at an angle to see a better picture)


    I don't have the Retina MBP, but from what I tried at the stores, I think I get strains from it that is similar (but much less problematic comparatively) to what I get from the iPhone 5. (I refer this as "Type 3" eye strain in my previous post)



    I'm trying to follow up with the tests on filtering the screen with a polarizer today. I don't have a proper linear polarizer at home, but managed to find an old pair of sunglasses. It is green tinted and polarized. I tried wearing it while using the iPhone 5 for about 20 min and it seems to be quite effective in cutting down the strain.


    I'm still thinking what exactly has helped, it could be the polarizer, the green tint, the UV cut or maybe just simply reduction of brightness.

  • Eric Leung1 Level 1 Level 1 (5 points)

    LovesDogs0415, can you try your new iPod Touch with have a polarized sunglass and see if it helps too?

    I guess it is using the same type of screen like the iPhone 5.


    Thanks a lot!

  • Gurm42 Level 1 Level 1 (0 points)

    My guess about those devices is that the amount of LED intensity that is required to get through that dense a pixel grid is higher than before. At first the iPhone4 gave me more trouble than my previous device, but I don't know if it settled down or I got used to it. Either way it's fine now. The 5 has even more pixels... and a bigger screen... so more LED intensity required, if I had to hazard a guess. I did experience some discomfort when playing with the new Lumia ... whatever was the latest and greatest Windows Phone in June. Not the 920, but the one just prior to that. It made me feel icky to look at. Again, maybe the LED?

  • LovesDogs0415 Level 1 Level 1 (0 points)

    I returned it, but my husband has an iPhone 4 I think.  I will try that.  Will let you know.

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