No-PWM Monitor Recommendation

[wassja]

http://www.youtube.com/watch?v=pl7EWrvyAcs

In this video you can clearly see the flicker of the ZR2440W, which has a measured flicker frequency of 430 Hz. It was taken with a camera with a shutter speed of 1/1000 sec. So with this shutter speed you can detect, if you see no flicker on the camera, either if the PWM is off completely (as at full brightness of the ZR2440W in the video) or if it's exceeding 430 Hz by a large number. It's foolproof either way as it can detect any flicker of below 430 Hz with 100 % certainty. And flicker of above 430 Hz poses no danger of being subliminally perceived and causing symptoms.

Additionally, If you knew exactly with what shutter speed 350 Hz were still barely flickering , but 380 Hz were invisible, then you could go for the LCD with PWM of not lower than 380 Hz in a store by not seeing the flicker on the camera. For that you would need to have a 350 Hz flickering LCD with a very high duty cycle and a 380 Hz LCD with the same duty cycle and you would need to experiment by trying to lower the shutter speed until 350 Hz were barely flickering and 380 Hz flicker were invisible to the camera. With the shutter speed result you would be able to detect any flicker of below 380 Hz but everything above it would look flicker-free.

This theory only works if the camera's LCD display displays the same visible flicker lines as it does on the recorded video. But if it doesn't, then you could just record the video and play the recording on the camera immediately to see if the LCD flickers while you're still in the store. And it would still be a good flicker detector.

The only things we need is a camera where we can set the shutter speed and to know what shutter speed to put. Perhaps there's an easier way of finding out the right shutter speed. One thing we know for certain, it's that 1/1000 sec. of shutter speed detects any flicker below 430 Hz.

 

[ButtMagician]

TFTCentral also described a method of detecting PWM using a digital camera:

http://www.tftcentral.co.uk/articles/pulse_width_modulation.htm

 

[ButtMagician]

Supposedly the new A06 revision of Dell U2312HM doesn't use PWM either, but I'm not sure how much we can trust the video:

http://www.youtube.com/watch?v=8gARC5Wf6FE

 

[wassja]

I mentioned the Samsung S27B970D earlier and I have to make a correction:

There are conflicting PWM measurements of this LCD. tftcentral.co.uk claims that it uses no PWM brightness control, while prad.de says it has no PWM at full brightness, but 180 Hz PWM at lower brightness. A person has bought the display and says he can only look at it when it is set to 100% brightness with no PWM. So it turns out prad.de is right and the LCD uses PWM at any brightness less than 100%.

 

[dezz]

@wassja: They were searching for the signs of PWM at 100% brigtness? Funny. Probably no one use PWM at 100% brightness.

 

[wassja]

I think both did correct tests and got different results because the same monitor may have different PWMs. It seems that there is no guarantee that you will have an LCD with a good PWM value if you buy one of the LCDs others have measured to be OK.

 

[Mali Bashi]

I'm another sensitive guy who stopped watching TV and even quit a job to escape burning headche caused by the poor-quality CRTs typically used in offices at the time (1991) :'( Things got bearable again with high-frequency CRT in the mid 90ies and good with TFT becoming standard some years later. Now with LED backlight the headache is back!

I'm very grateful to this forum since I found my new monitor (EV2436W) thanks to your good research :thumbsup: after months of looking and trying. I'd like to add some experience:

The safest group:
2) EIZO EV2436W
[...]
On forums you get the information that they only use no PWM if brightness is set to above 20%.

I can confirm that my Eizo EV2436WFS uses no PWM until 20% brightness. Below that threshold the PWM kicks in, and it's nasty because Eizo use a low frequency. I needed to disable the EcoView features since they keep lowering the brightness below 20% if the ambient light is less than daylight.
For office work I am happy with brightness set to a constant 21% with the universal and neutral sRGB preset which gives a steady picture without PWM and causes neither strain on the eye nor headache. For movies I switch to the bright movie preset.
Great monitor, and apparently the only 24" 16:10 LED on the market presently which can provide what I need.

HP ZR2440W
The LCD HP ZR2440W is measured to have a PWM frequency of 430 Hz. This is high enough to not cause any problems.

"not cause any problems", well... after reading this post I tried the HP ZR2440W first, before I purchased the Eizo. While it is true that the PWM flicker of the HP is not visible to the naked eye, it did cause me a burning headache within 30 minutes every time I used the monitor. I returned it with regret, after trying to convince myself for a week that I'm imagining things or the headache has other reasons - but no, it is a very particular burning pain that I had only when working on this monitor.

I have no such problems on my older TFT with CFL-backlight (a Samsung 2443BW which I use in my full-time office job), neither with my private Eizo. Otherwise the HP is a very good piece of equipment en par with the Eizo but for less money.

 

[wassja]

Hi Mali! I'm very happy you found a good monitor. I would like to write my opinion about what probably happened with the HP ZR2440W. I think they simply lowered the PWM frequency on the new versions of that monitor. I have been it touch with a person who bought it and said it helped him greatly, but later a different person bought the same monitor and it failed as a solution. I asked him to reduce his monitor's brightness to zero and to check with a camera phone for moving lines, an indication of a low PWM frequency, and he saw them. I'm pretty sure you shouldn't be able to see moving lines on a camera phone if the PWM is really 430 Hz (I think the cameras are more or less the same on every phone). So afterwards I divided the list into 3 groups and only recommend the monitors which manufacturers themselves claim to be PWM-free under certain conditions.

 

[Phol]

How about laptops? I am in desperate need for a laptop that does not hurt my eyes. I move a lot for business purposes and a monitor is not appropriate for me.
I was in need to change my laptop and purchased a Macbook Pro (first time in Apple). I cant look at the screen more than 15 mins. Eye strain, headache, and nausea come in. I experienced the same with a Dell laptop (led as well).
Does anyone know of a laptop that is more friendly to the eyes?
I am thinking to purchase a used laptop in ebay if no new laptop is there with a screen tolerable to my eyes.

Thanks

 

[wassja]

There is something mysterious about Apple lately. Measurements show no easily detectable PWM in their newest devices, and yet people experience the same flicker symptoms as PWM used to cause. One person, among others, found about 80% relief from his symptoms when he changed the screen resolution to a non-native one. I've also read about an upgrade from XP to Windows 7 being the reason for experiencing symptoms. There is also a case of someone being fine with Windows 7, but having problems after upgrading to Windows 8. This suggests a new problem other than PWM. From the information I think the fault for the symptoms is not the OS, but some other element. I suggest that element is the drivers. So I would call this a software problem.

People may mistakenly think there can only be one problem causing eye pain, headaches and such. I just wanted to say I know of two, one of which isn't completely identified.

The only advice for Macbooks is to try some non-native screen resolutions, downgrade the OS somehow or do something with the drivers. I never used a Macbook so I don't know what is possible on it.

 

[wassja]

Found an interesting video: http://www.youtube.com/watch?v=ycKzTDnTYTQ

I learned from it that one can change the PWM frequency with a special software called "IntellPWMControl" on the Thinkpad T410. I think this software might work on other Thinkpads, but that's just what I think. It didn't work on my Asus netbook by the way. It is possible to download it here, but the site is in Russian and it is tricky to download it because one needs to choose an advertiser and watch an advert for 30 seconds: http://rusfolder.com/23805792

Thinkpad T410 + IntellPWMControl = opportunity to set a 500 Hz PWM frequency.

I have seen people solve their problems by finding an LCD with 360 Hz PWM. This convinces me that 500 Hz are safe.

 

[Phol]

Have you any smartphones that does not cause eye strain? I purchased Galaxy SIII some time ago and the eye strain and headache were intense after use for some time. So i quit using it.
I read that Nokia Lumia 920 provides flicker free images and videos. Does anybody know if this is this relevant to PWM and reduces the problem for sensitive people? Any other smartphone that is comfortble for the eyes?
Thanks

 

[wassja]

http://cellphoneaddict.com/nokia/nokia-lumia-920-review/

"Adjust the brightness by using pulse width modulation (square wave with 100% amplitude) at a high frequency (710 Hz), so the flickering backlight dimmed sight."

If this is correct and applies to all Nokia Lumia 920 phones, then I believe it is worth trying it.

 

[Dacq]

In future LED-backlit LCD screens will be replaced with all LEDs, so will the problem remain?

 

[Mark Rejhon]

I have seen people solve their problems by finding an LCD with 360 Hz PWM. This convinces me that 500 Hz are safe.

Alas, 500Hz may not be enough in certain cases:

Phantom Array Effect / Stroboscopic Effect
- http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1538&context=tpr (500 Hz detected)
- http://www.lrc.rpi.edu/programs/solidstate/assist/flicker.asp (300 Hz detected)
- http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-Flicker.pdf (10,000 Hz detected)
- http://cormusa.org/uploads/2012_2.10_Bullough_CORM_2012_Stroboscopic_Effects.pdf
- http://people.ds.cam.ac.uk/ssb22/lighting.html
Synopsis: Humans can indirectly detect a 500 Hz flicker via the “phantom array” effect: A fast moving flickering light source in a dark room, appears as a dotted trail instead of a continuous blur. This can also occur when rapidly moving/rolling eyes in front of flickering lights in a darkened room (e.g. old LED alarm clocks, neon lights, unrectified LED decoration light strings). Flicker all the way up to 10,000 Hz was indirectly detectable in some studies, in certain situations.
___

This is easier for point sources of light; which is easier than a large display; since there's less opportunity for a phamtom array effect to occur. But the indirect detection threshold can actually be north of 500 Hz. Also, PWM artifacts can still be very ugly looking even at 500 Hz; you need several kilohertz to make PWM motion artifacts completely disappear.

 

[Mark Rejhon]

Some people get eyestrain because of too much brightness...
Some people get eyestrain because of PWM itself...
Some people get eyestrain because of motion blur...
Some people get eyestrain because of both (PWM + still too bright)...
Some people get eyestrain from PWM artifacts (see LCD Motion Artifacts 101)
Some people get eyestrain from PWM flicker instead.
Or a combination thereof...

(PWM motion artifacts look like: ...)

Some people found PWM is bad because of excess brightness. Many LED monitors are so bright, even at Brightness=30%, so having excess brightness combined with PWM, amplifies the eyestrain problem.

Several users noticed that CRT flicker at high refresh rates (at 120 Hz) does not bother some people's eyes, while PWM (even at 360 Hz) does. So there are additional factors in play; such as ugly-looking PWM artifacts, as well as the excess brightness combined with PWM. It's important to try to find out what your eyestrain is truly caused by. This also applies to phones too as well.

The use of a single strobe per refresh (e.g. CRT, LightBoost) leading to zero artifacts (no PWM, no motion blur), also play a factor in humans that aren't flicker-sensitive (e.g. eye strain caused by motion blur instead of PWM).

It's fascinating vision behavior, something a scientist should eventually research.
It will be a long time before we have an Ultimate display that fixes all problems.