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causticphoton
Fanfold Paper
Posts: 7
Registered: ‎10-21-2016
Location: CA
Views: 2,443
Message 1 of 10

P50 FHD 1080 backlight PWM control

My P50 20EN0013US has the 1080 FHD panel, and I found the backlight is really distracting at less than 100% brightness thanks to the default PWM frequency of 200 Hz.

 

It turns out that the default PWM frequency might be due to the Intel HD drivers. I found a utility on the web to adjust this frequency and now I enjoy up to 20000 Hz PWM frequency resulting in a flicker-free display. Yes!

 

For anyone else out there who gets headaches from the default PWM frequency, try this out. It worked for me. I tried several utilities, but this was the only one that worked for me on Windows 10 Pro 64-bit.

 

https://github.com/tpurtell/PWM

 

I should also mention that this utility must be run after every reboot because the Intel HD driver resets the PWM frequency back to 200 Hz on startup. 

microfishd1
Token Ring
Posts: 267
Registered: ‎02-19-2015
Location: US
Views: 2,400
Message 2 of 10

Re: P50 FHD 1080 backlight PWM control

Thank you! In the unfortunate event that my screen has noticeable PWM, I will try this out!

Do you hear screen "whine" at high Hz?
Does it work on 7Pro 64-bit?
Will it stay open across Standby/Hibernation?

Thanks!
-----------IBM T40: XP PRO SP3, 14.1" 4:3 display, 512MB DDR RAM, 40GB HDD, ThinkLight, DVD.
Lenovo Ideacentre H215: AMD Athlon II X2 215, 500GB HDD, 4GB DDR3 RAM, 64-bit Win7, AMD 760G.
P50 i7, M2000M, 1x16GB RAM, 1080p non-touch, 512GB SSD, 500GB HDD, Backlight, No WWAN, No PWM, No Raid.
DAVader
802.11n
Posts: 108
Registered: ‎09-05-2016
Location: US
Views: 2,379
Message 3 of 10

Re: P50 FHD 1080 backlight PWM control

I thought the 4K display had PWM control, but the FHD didn't (notebookcheck.net review):

 

Screen Flickering / PWM (Pulse-Width Modulation)

To dim the screen, some notebooks will simply cycle the backlight on and off in rapid succession - a method called Pulse Width Modulation (PWM) . This cycling frequency should ideally be undetectable to the human eye. If said frequency is too low, users with sensitive eyes may experience strain or headaches or even notice the flickering altogether.
Screen flickering / PWM not detected
________________________________________________________________
P50 - Xeon E3-1535M v5 - 32 GB RAM - FHD display - Quadro M2000M - Win7 x64
causticphoton
Fanfold Paper
Posts: 7
Registered: ‎10-21-2016
Location: CA
Views: 2,369
Message 4 of 10

Re: P50 FHD 1080 backlight PWM control

Filmed with an iPhone 6s.

 

https://youtu.be/iK4wfvN1OxE

 

causticphoton
Fanfold Paper
Posts: 7
Registered: ‎10-21-2016
Location: CA
Views: 2,368
Message 5 of 10

Re: P50 FHD 1080 backlight PWM control

The utility I used to change the PWM frequency keeps the changes persistent across standby but not a power cycle. Don't know about hibernation or Windows 7.

Phil__C
Token Ring
Posts: 176
Registered: ‎01-01-2016
Location: US
Views: 2,348
Message 6 of 10

Re: P50 FHD 1080 backlight PWM control

Does the PWM issue appear while using the Nvidia discrete graphics only (Optimus off)?

 

jsa
SCSI Port
Posts: 41
Registered: ‎06-21-2016
Location: AU
Views: 2,338
Message 7 of 10

Re: P50 FHD 1080 backlight PWM control


@DAVader wrote:

I thought the 4K display had PWM control, but the FHD didn't (notebookcheck.net review):

 

Screen Flickering / PWM (Pulse-Width Modulation)

To dim the screen, some notebooks will simply cycle the backlight on and off in rapid succession - a method called Pulse Width Modulation (PWM) . This cycling frequency should ideally be undetectable to the human eye. If said frequency is too low, users with sensitive eyes may experience strain or headaches or even notice the flickering altogether.
Screen flickering / PWM not detected

Lenovo are dirty rotten cheats. They send notebook check a different screen part number compared to us worthless customers.

 

My FHD flickers below 100% brightness. It is a different screen part number compared to the notebook check screen part number.

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microfishd1
Token Ring
Posts: 267
Registered: ‎02-19-2015
Location: US
Views: 2,326
Message 8 of 10

Re: P50 FHD 1080 backlight PWM control

As noted elsewhere on this forum, Lenovo uses three (3) or more different part numbers (from three different vendors/manufacturers) for "their" 15.6" 1080p P50 screen.
At least one of these parts has been documented to NOT have PWM, but at least one of these parts has been documented TO have PWM.
As far as I can tell, the part that you get depends on the box of screens on top at the assembly line when your machine is assembled. Some people have received the same PN as the model that notebookcheck.net reviewed. Others obviously did not.

-----------IBM T40: XP PRO SP3, 14.1" 4:3 display, 512MB DDR RAM, 40GB HDD, ThinkLight, DVD.
Lenovo Ideacentre H215: AMD Athlon II X2 215, 500GB HDD, 4GB DDR3 RAM, 64-bit Win7, AMD 760G.
P50 i7, M2000M, 1x16GB RAM, 1080p non-touch, 512GB SSD, 500GB HDD, Backlight, No WWAN, No PWM, No Raid.
improwise
HDMI
Posts: 181
Registered: ‎06-14-2016
Location: SE
Views: 2,052
Message 9 of 10

Re: P50 FHD 1080 backlight PWM control

This is an interesting thread. How come the PWM settings are set so low when it obvioulsy seems like you can change it to anything you want? There must be some drawbacks here?

 

Also, I recall hearing about some kind of utility that would "fake" the screen being dimmer than it really is, in order not to have PWM triggered by actually lowering the screen brightness. Anyone have tried such a tool (or perhaps can remember the name of it?).

microfishd1
Token Ring
Posts: 267
Registered: ‎02-19-2015
Location: US
Views: 2,024
Message 10 of 10

Re: P50 FHD 1080 backlight PWM control

Are you maybe thinking of "Dimscreen.exe" (v1.1)? I first found it years ago when my laptop wouldn't get dark enough. It is an autohotkey script, I believe, and might work to fool PWM.
-----------IBM T40: XP PRO SP3, 14.1" 4:3 display, 512MB DDR RAM, 40GB HDD, ThinkLight, DVD.
Lenovo Ideacentre H215: AMD Athlon II X2 215, 500GB HDD, 4GB DDR3 RAM, 64-bit Win7, AMD 760G.
P50 i7, M2000M, 1x16GB RAM, 1080p non-touch, 512GB SSD, 500GB HDD, Backlight, No WWAN, No PWM, No Raid.

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