Which iMacs use pulse width modulation?

sevenall

macrumors newbie
Original poster
Oct 21, 2010
9
4
Contacted Apple support as I couldn't find any sources online that provided a definitive list of all of the current iMacs and whether they used Pulse Width Modulation (PWM) in their displays.

They were unable to "locate that information". They escalated the call to a supervisors but nobody was able to tell me if PWM is used in their displays.

Many people's eye are sensitive to this so it's an important factor when making a purchase.

Does anyone have more information?
 
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jagolden

macrumors 65816
Feb 11, 2002
1,029
681
Contacted Apple support as I couldn't find any sources online that provided a definitive list of all of the current iMacs and whether they used Pulse Width Modulation (PWM) in their displays.

They were unable to "locate that information". They escalated the call to a supervisors but nobody was able to tell me if PWM is used in their displays.

Many people's eye are sensitive to this so it's an important factor when making a purchase.

Does anyone have more information?
I wasn’t aware that iMacs were OLED. Not that familiar with PWM but thought it was confined to OLED’s.
Help me learn.
 

mikehalloran

macrumors 68000
Oct 14, 2018
1,600
390
The Sillie Con Valley
I wasn’t aware that iMacs were OLED. Not that familiar with PWM but thought it was confined to OLED’s.
Help me learn.
1. Read something on the internet.

2. Don’t learn anything about it.

3. Worry

4. Post your concerns


No displays use PCM at full brightness. Some Apple displays use it when brightened hits 50% or lower. Supposedly, the iMac Pro is one of them but I’ve never seen confirmation of this. It’s never been reported in any other iMac

Many are trying to make a big issue about this on the iPhone X but according to Apple, it doesn’t kick in till the screen brightness reaches 35%. Who has their screen that low?
 

jagolden

macrumors 65816
Feb 11, 2002
1,029
681
1. Read something on the internet.

2. Don’t learn anything about it.

3. Worry

4. Post your concerns


No displays use PCM at full brightness. Some Apple displays use it when brightened hits 50% or lower. Supposedly, the iMac Pro is one of them but I’ve never seen confirmation of this. It’s never been reported in any other iMac

Many are trying to make a big issue about this on the iPhone X but according to Apple, it doesn’t kick in till the screen brightness reaches 35%. Who has their screen that low?
Actually I use my Max between 30 - 35.
Don’t need it brighter than that unless using in super bright sunlight.
Luckily I’n not affected by the issue that does seem to be overblown by some.
 

sevenall

macrumors newbie
Original poster
Oct 21, 2010
9
4
Actually I use my Max between 30 - 35.
Don’t need it brighter than that unless using in super bright sunlight.
Luckily I’n not affected by the issue that does seem to be overblown by some.

The subtle flicker caused by PWM is a real issue for some people (like me). It leads to severe headaches and nausea when looking at a display using this technology. It's frustrating that it's not easy to find the information on displays when considering a purchase.

The iMac Pro does use PWM (they information is available online) but not the 2019 iMac (for example).
 

mikehalloran

macrumors 68000
Oct 14, 2018
1,600
390
The Sillie Con Valley
The iMac Pro does use PWM (they information is available online) but not the 2019 iMac (for example).
I’ve read it and don’t trust the source of that information. It’s obvious that someone’s guessing.

I’ve run my iMP down to 10% to see and don’t believe it. Since the iMP and 2015–2019 all use the same LG display, why would Apple use PWM in one and not all? There is no reason to believe they do.
 
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Moonjumper

macrumors 68010
Jun 20, 2009
2,002
1,557
Lincoln, UK
I wasn’t aware that iMacs were OLED. Not that familiar with PWM but thought it was confined to OLED’s.
Help me learn.
PWM is common on LCD displays. What happens is the backlight is turned on and off quickly to lower the brightness to the level set. The lower the brightness, the more time the backlight is off.

It was not such a problem with the older CCFL backlights as they had an afterglow, so the on/off cycle was not perceptible in almost all cases. But LED backlights do not have the glow, so it can be an issue. If the on/off cycle is not fast enough for the individual (it is wrong to say it is overblown because it doesn't affect the person saying so), the flickering can be perceived (not quite the same as actually seeing it, just being affected by it). The lower the brightness, the greater the off period of the backlight, so the more perceivable it is. The flicker does not have to be matched to the screen refresh rate. Apparently it can vary from 90Hz to 400Hz, so not all PWM screens are the same.

The alternative of lowering the LED voltage is more expensive, can have a shorter lifespan, and is more difficult for getting colour accuracy, so that is why PWM has remained on many monitors.

I used to be affected by the flicker on CRT monitors if they were not set right (I used to turn up the refresh rate to the highest possible so it was not a big issue if it allowed 96Hz or higher). But my frequency of migraines dropped off a cliff as soon as I switched to LCD monitors. That maybe a coincidence as there were other changes about the same time, but it probably helped.

When I got my first LED backlit monitor, I made sure to get a flicker-free model. I wish such information was more freely available from Apple about their screens.
 

jerwin

macrumors 68020
Jun 13, 2015
2,460
4,452
Many are trying to make a big issue about this on the iPhone X but according to Apple, it doesn’t kick in till the screen brightness reaches 35%. Who has their screen that low?
phoitographers, among others

Depending on the time of day, I may have my imac set to about that level. My secondary display is set to minimum brightness. Haven't gotten around to replacing it with somehing more accurate.
I don't think that I'm sensitive to pulse width modulation, though.
 
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mike.coulter

macrumors regular
Jun 10, 2008
179
23
Cardiff
This is one reason I purchased the iPhone XR rather than the XS.

Companies should clearly point out which products use this method of screen dimming, as it could easily affect people without them knowing the cause.
 
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jagolden

macrumors 65816
Feb 11, 2002
1,029
681
Contacted Apple support as I couldn't find any sources online that provided a definitive list of all of the current iMacs and whether they used Pulse Width Modulation (PWM) in their displays.

They were unable to "locate that information". They escalated the call to a supervisors but nobody was able to tell me if PWM is used in their displays.

Many people's eye are sensitive to this so it's an important factor when making a purchase.

Does anyone have more information?
Almost sounds like they are hiding from the issue.
Even though not an immense problem, it is affecting enough people that they should stop implementing it as they do. I’ve read many other posts where people have pointed to other companies using it but in a way that does not cause people problems.
Might not be able to eliminate it completely, but sounds like it could be done in a way to help a lot of others.
 

spraycansoul

macrumors newbie
Apr 12, 2019
22
3
Anyone able to confirm if the iMac 2019 has PWM?

I know on notebookcheck it states the iMac 2015 doesn’t. I’m convinced I heard Apple went from Dell to LG for displays at some point but can’t confirm.
 

Zandros

macrumors regular
Sep 1, 2010
110
61
Anyone able to confirm if the iMac 2019 has PWM?

I know on notebookcheck it states the iMac 2015 doesn’t. I’m convinced I heard Apple went from Dell to LG for displays at some point but can’t confirm.
Dell does not make (and to the best of my knowledge never has made) display panels.