PWM and other Causes of Flicker

Discussion in 'Hardware' started by kurt corbin, Sep 3, 2019.

  1. kurt corbin

    kurt corbin Scribbler - Standard Member

    Messages:
    168
    Likes Received:
    61
    Trophy Points:
    41
    According to oled-info.com, "Several studies claim that about 10% of people experience discomfort when viewing PWM displays (while the rest are either completely okay or with some very mild discomfort). Some people suffer very badly and the flickering may result in other health issues."

    PWM is supposed to be the main cause of flicker, but according to notebookcheck, “some devices do not use PWM at all, but still showed a measurable brightness flickering during our review (e. g. [from] poor shielding of the power adapter).”

    Dear notebookcheck: So how do you determine what the cause is?

    Notebookcheck continues: "The problem is that it’s a standard industry practice to use displays [i.e., panels] sourced from multiple manufacturers for the same laptop. So while the unit we test might be PWM free, the next one under the same model name might have PWM - while they should be identical on the specsheet, in reality, they are not...This is a problem impossible to solve for us. We at Notebookcheck cannot test every single Notebook on earth and its almost always impossible to tell how many different display panel variations there are for a product, because the manufacturers are mostly intransparent about this stuff...In the end, it’s the manufacturers who are not transparent about their products. It’s their task to make more honest spec-sheets and inform people about their products."

    Exactly. Look at how Lenovo's sales rep responded to me:

    Andersson Steve M.: Hello, thanks for contacting Lenovo Sales. My name is Andersson Steve M. (Rep ID: 2900729623). At the conclusion of this chat, there will be a brief, two-question survey, scoring from 1-10 where 10 is the best. Please be sure to ask about our flexible payment options!

    Me:
    I need c940 14" info.

    Andersson Steve M.:
    Welcome to Sales Chat Department. How can I assist you with your purchase today?

    Me:
    There are 5 displays available?

    Andersson Steve M.:
    Yes

    Me:
    Do any use pwm?

    Andersson Steve M.:
    all of them

    Me:
    Notebookcheck says the 1080p glossy does not.

    Andersson Steve M.:
    Well, that is the information I have about displays

    Me:
    I'm not even sure what it means. What does pwm mean?

    Andersson Steve M.:
    Pulse-width modulation

    Me:
    Is that good or bad?

    Andersson Steve M.:
    That is good because it improve the resolution and avoid you headache

    Me: Have a nice day!

    Note the level of English: ...it improve the resolution and avoid you headache!
    Also note that at the time of this conversation there were actually only 4 display options listed on Lenovo's website: 1080p and 3840p, with or without anti-glare. A couple of days later, that was changed to indicate that there are only 2 display options. The anti-glare options were removed.

    So to find out what panel your display has, you can do some detective work to make an educated guess before you buy, as I did here for the Lenovo C940-14iiL:

    3840p 500-nit glossy HDR (supplier?) pwm = ?
    The 3840p 500-nit glossy HDR in the S940 is the AUO B140ZAN01.3, and it also has pwm = 0. After browsing through the list of Lenovo displays laptopmedia.com has made, I think that's the only 3840p 14" display Lenovo uses. Note, however, that laptopmedia measured it at 445 nits, while notebookcheck measured it at 536.

    Or you might put the HWiNFO utility on your flash drive and run it on a showroom computer at Best Buy or the like. That is the suggestion of laptopmedia.com for finding the part number of a panel. Or you could take the panel out and have a look. Or you could use your oscilloscope. Or do the pen-wave test or the like. Then return the thing if you don't like the results.

    Notebookcheck claims that PWM is a necessary evil: “New technology such as what is found in smartphones is too small and designed to use too little power to utilize any alternatives such as analog controllers.”

    Dear notebookcheck: Then why are there numerous smartphones listed on your website with PWM = 0? And you also say the Razer Blade 15 Studio Edition with OLED has PWM=0.

    Notebookcheck continues: “…manufacturers such as Xiaomi and OnePlus decided to offer DC dimming in their devices with AMOLED displays on a trial basis. We have already examined the effects of the new technology (called Flickering Protection by Xiaomi)…”

    Actually, Xiaomi's DC dimming is used in combination with PWM. Moreover, it seems to be doable with a firmware update.
     
    Last edited: Dec 3, 2019
  2. kurt corbin

    kurt corbin Scribbler - Standard Member

    Messages:
    168
    Likes Received:
    61
    Trophy Points:
    41
    Looks like this new DC dimming is not done with hardware:

    "DC dimming control uses a DC voltage between 0 and 10 to control the light output of the OLED panel. As the voltage goes up or down, the corresponding 0-10V dimmable driver matches the light output of the fixture to increase or decrease up to a certain percentage.....The Mi 9 and Reno use a software pattern to reduce the low-brightness strobe. Xiaomi is reportedly still developing a new pure hardware DC dimming."

    https://www.oled-a.org/oledrsquos-c...g-to-improve-low-luminance-images_051319.html
     
    WillAdams and thatcomicsguy like this.
  3. kurt corbin

    kurt corbin Scribbler - Standard Member

    Messages:
    168
    Likes Received:
    61
    Trophy Points:
    41
    Update: I have just learned that PWM is not an inherent attribute of the display's panel. Rather, it's determined by the display's controller. See the thread on the Razer Blade.
     
    Last edited: Dec 4, 2019
    thatcomicsguy likes this.
  4. thatcomicsguy

    thatcomicsguy Pen Pro - Senior Member Senior Member

    Messages:
    3,212
    Likes Received:
    2,259
    Trophy Points:
    231
    I've not taken a screen apart recently, so I don't know exactly what modern design solutions are in style right now, but a few years ago, there would be a whole extra board to handle the backlight, and you could see where it was and the wires it used to connect to the light/s.

    I would imagine that today, the video and backlight controller, (and who knows what else), would all be integrated with laptops and tablets.

    But yeah, the LCD and signal controller have nothing to do with the backlight. That's somebody else's department.

    Unless, of course, we're talking about OLED, (where each pixel is its own light source) in which case there would have to be a completely different design going on. I would imagine that brightness control through PWM on OLED would be the preferred (easier) way to go. Samsung is apparently known for using it as their main strategy. I keep my tablet on 100% brightness, though, I would also imagine that this wont be a solution as new techniques come along, (where PWM may be used regionally on some parts of the screen which want to display shadows even while the whole screen brightness is technically set to 100%.)

    Basically, I really like IPS screens, and will stick with them for the most part if able.

    Our Tech Overlords want us all to be zombies eventually. :)
     
  5. kurt corbin

    kurt corbin Scribbler - Standard Member

    Messages:
    168
    Likes Received:
    61
    Trophy Points:
    41
    I don't understand where the panel's controller is. When Razer Blade orders an SDCA029 OLED panel from Samsung, does it come with the contoller attached? Then Razer blade substitutes their "custom" contoller, as desertlap calls it, to eliminate the PWM? If that is true, then it's futile to try to figure out which panel a display has in order to make a purchase decision. Rather, you have to figure out what controller it has in the final configuration. So who makes the no-PWM controllers, and what are their part numbers, and does the HWiNFO utility give them to you, because surely the computer companies won't.
     
    Last edited: Dec 5, 2019
  6. thatcomicsguy

    thatcomicsguy Pen Pro - Senior Member Senior Member

    Messages:
    3,212
    Likes Received:
    2,259
    Trophy Points:
    231
    Yeah.., anybody interested for long enough in what's going on "under the hood" will have run into that road block before. The wonderful Internet provides an ocean of information.., except for when it comes to industrial proprietary parts and patent secrets and stuff they just don't feel like sharing out of house. Other bits of information you can get, but only if you're tagged in the engineering community and know people who can share documents on private and semi-private networks. (For instance, just yesterday, I was curious and wanted to get hold of a copy of the international standard regarding nanometer light wavelengths for different colors as they pertain to industrial lighting and LEDs. Everywhere I looked, you have to pay more than $100 for a copy of the .pdf file! No thanks; I'm not that curious.)

    Anyway, with OLED, I haven't done any research, but if the same engineering techniques apply, then you'd probably get boards where the manufacturer has integrated control chips into the screen.

    I know when I was buying IPS screens on their own, they would always come with a floppy bit of plastic attached which had complicated surface mounted control chips stuck to it. That was attached to the edge or on the reverse side of the glass screen. The computer's video controler board would then plug into that with a standard cable connector. This would imply that the screen is in charge of how everything works and the controller board just sends what it wants displayed.

    Now in the new era of OLED.., I would imagine that if a company like Razer wants to do something different wrt brightness control, that they would give their specifications to their supplier, (to Samsung, for instance), and then Samsung's in house engineers would produce the electronics necessary to satisfy the customer's requirements, and then deliver the product.

    For those of us on the outside of this industrial marvel, we have to look for scraps of information which trickle down, and perform our little video flicker tests with cameras and such. There are some dedicated websites which deal exclusively with the PWM and flicker question, and some of those guys have probably been at it long enough to have made contacts deeper within engineering circles than the casual explorer has access to, but I haven't checked recently.

    I'm sure that by the time I'm back in the market for a non-flicker screen, the technology will have evolved beyond where it is today and the problems will be all shiny and new, requiring new paths of exploration to be bushwhacked!
     
    Last edited: Dec 5, 2019
    kurt corbin likes this.

Share This Page