Here is a webpage of a guy testing different monitors for PWM by using a photodiode and an oscilloscope. I will try to do the same here, the webpage is in bulgarian however, just watch the videos.
There is a video in there that shows him using a software which actually increases PWM on a monitor. It is called IntelPWMcontrol and works only on intel graphics cards with LED backlights. It took me a while to find this software online. And one has to be really careful when downloading sth from a website in russia.
ArtechokiQ, great inputs, thank you for the expertise.
With all of the dithering, Hz and 10 bit or whatever monitor issues how do you explain getting the same exact physical reaction to any overhead LED lighting? What is the same about these two technologies that would both cause migraines and Vertigo? Here is an example of the lighting that removed me from work, I find it to be intolerable within seconds:
All light sources that derive their power from the AC main frequency are flickering one way or the other. LEDs are bad because of the depth of modulation which is worse than all otherlight sources.
LEDs react to 60Hz quickly. (Actually they will flicker at 120Hz). LED completely stops producing photons when its off. Regular lightbulb and fluorescent emit photons even if they are off.
So you can think of a LED as something that switches literally from completely black to superbright.
But a picture speaks hundred words, so I want you to look at the following article:
or try this which is the same:
Go to page 7and look at the flicker wave of a regular 60W A19 incandescent bulb, compare that wave with the wave of the "AC LED MODULE" on page 8. You can see how tall or deep the LED wave is!
From 2009 to 2010 I believe the EPA (U.S. Environmental Protection Agency ) has required the LED lights to have a frequency of minimum 150Hz. But then under pressure from industry they reverted back to 120Hz. There are LED lights that are driven by higher frequencies but I guess we are the only ones who can sense that!
here is another link:
I myself have no problems with Iphone 4s but with a new IPad things are really bad. Symptoms with the new Ipad are somewhat different then anything else. They feel more brutal and occur faster than anything else (within seconds) . Note they both use LEDS. I also have tried a TN panel monitor which is 120Hz namely samsung 2233rz which is actually CCFL, and the symptoms I get with the Samsung are very close to the new IPad. So I doubt our problems are specifically related to LED. They are related to all lights even incandescent. It is just that the depth of waves emmited by incandescent lights are very shallow whereas with LED they are very deep. CCFL lights are also deep but they are not that steep as LED waves. This is mostly related to flicker due to AC. (I guess we should have listened to Edison instead of listening to Tesla).But then I am also clueless with my own monitor NEC-231wmi which does not use PWM at full brightness and it has 82hz refresh rate and troubles me. All this is little more complicated than we think, at the core it is flicker. I am just tired a little of all this suffering we have to endure. It is really unbearable sometimes. There are times I wish I was born centuries ago!
Please dont think I am completely right I am prone to saying little mistakes here and there.
Frequency matters, and depth of (or modulation of waves) matters as well. Intensity matters.
So to wrap it up:
They all flicker if connected to AC. Question is at what frequency? How much is really bothering us? 60Hz, 120Hz, multiple of these?
I have no problem with newly installed lights at my work: Fluorescent at around 40000Hz
I had huge problems with Fluorescent with Magnetic ballast at around 60Hz
I had huge problems with CRT old style TV or computer monitor even if run at 120Hz
I had huge problems with LCD computer that are 60Hz with CCFL
I had some problems with LCD TV at 60Hz with CCFL
I had little problems with LCD TV at 120Hz with CCFL
I had little problems with LCD TV at 240Hz but then almost no problems when brightness is at 100%. with CCFL
However I can understand the point that Jessiah1 is making. I would get more problems if I start using the TV's as computer monitors. Then they start to bother me more. Is it a focusing problem or are we simply focusing our eyes and allowing more white light enter our eye, that I dont know.
I am not sure what Benq is doing now by introducing new computer monitors without PWM. Are they having their LED's connected to DC which would mean no flicker, that I dont know. Nevertheless the LCD panels themselves they are still oscillating. I am just curious now how much was PWM contributing to our suffering.
And for some darn reason my little iphone 4s does me no harm! Go figure.
If nothing else I ll convert my Kindle (Eink) into a monitor:
As a matter of fact there is a chinese company that will start soon making small eink readers that can be connected as computer monitors via USB.
Anyways folks good nite and sleep tight. Sleep seems to be best remedy! Make sure you go to sleep early, use all the daylight u can!
Thanks for all of the posts, I appreciate all of the information. The more I learn the more I realize how complicated this area is. I really wish that professional, paid engineers were doing as much research into this as people here are.
One thing that interests me is how these issues start. ArtechokiQ, Jessiah1 and myself have all had head traumas around the time we started having issues. We can't determine if they're connected. But it would be great to be able to crowd source information to see where these things start, what the triggers are and what the solutions are.
Hi ArtechokiQ, thank you for all the information that you have provided!
One thing I would like to point out is that other than flickering, there are very likely other causes for the serious eye strain that we are experiencing.
I believe one of the other causes is highly likely related to the blue of the LEDs. (I know not everyone here agrees with me on this)
A few observations that I have made regarding the recent Apple devices:
- All latest Apple devices don't seem to exhibit PWM flickering. I have tried the "camera swinging" method on many Apple screens that were produced in the recent years, and I can't prove the backlight of any of them to be flickering. (that however doesn't rule out the fact that the pixels are flickering at the matrix level)
- Not all LED screens are uncomfortable, my first generation 27" aluminium iMac, iPad 2 (early production batch) and all my iPhones before and including the 4S (early production batch) are comfortable to my eyes.
- The newer devices starting from the later productions of iPad 2, later productions of iPhone 4S and iPhone 5, etc. all seems to be uncomfortable at a level of being bad to super bad. And I cannot prove any of them to have flickering backlights.
- It kind of feels that the latest more energy efficient LEDs are more uncomfortable to the eyes. (maybe the newer LEDs emit more blue?)
- I have tried using filters to filter out some of the blue light from the displays, quite a lot of them feel noticeably better with the filter on, and I could use those displays much longer than without the filters, though usually I'm not able to completely remove the discomfort.
It appears that the screens that are not too uncomfortable to begin with works better with the filters.
- I have read articles saying that blue lights are harder for our eyes harder to focus. They also have a better peneration power than other colors in the visible spectrum, which makes them able to penerate much better through our cornea and hit right onto our retina. (sorry I didn't keep the links to the original articles that I read) That kind of match how I feel when I'm looking at the newer displays, especially for the iPhone 5. The light just seem to hit right onto my pain nerve even if I put the brightness to very low.
I was brought to this forum due to some pretty bad sickness from the flickering (at the matrix level, not the backlight) of my old MacBook Air, so I believe I know how that's like. However, the discomfort that comes from the latest Apple (and from many other brands too) devices are quite different, I firmly believe there is another cause for the serious eye strains other than just flickering.