Page 1 of 2 12 LastLast
Results 1 to 16 of 17

Thread: LED Backlight flicker - common & dangerous?

  1. #1
    Member
    Join Date
    Jun 2004
    Posts
    103
    Thanks
    0
    Thanked
    0 times in 0 posts

    LED Backlight flicker - common & dangerous?

    I became aware of the 'problem' of LED monitors flickering thanks to this YouTube video.

    This video put me off buying said monitor, and I recently purchased a ViewSonic VX2370Smh-LED 23" for a decent price.

    After doing a bit of further reading I see the 'problem' is caused by lowering the brightness on an LED LCD monitor (and how the tech works to do this) and isn't specific to this Dell.

    I've used my phone camera to look at my monitor and I see flickering similar to the YouTube video on the monitor I have bought.

    Now, I don't seem to obviously be able to detect the flickering with my eyes directly, but I've done some reading and some people say this can cause eye strain, etc.

    My eyes do seem to feel more tired when using the new monitor but I believe this could be A) Because I've read about the issue and the effects it can have B) I've gone from a 19" to 23" screen with brightness higher than I usually use (as I believe this causes less flicker from my reading).

    I'd be really interested to get any opinions as I am half tempted to return the monitor, and surely it has implications for many people who use these monitors if its all true.

  2. #2
    Senior Member
    Join Date
    Nov 2009
    Posts
    2,231
    Thanks
    578
    Thanked
    226 times in 184 posts
    • ik9000's system
      • Motherboard:
      • Asus P7H55-M/USB3
      • CPU:
      • i3-540, Prolimatech Megahalems, Akasa Apache 120mm
      • Memory:
      • 4x2GB Corsair XMS3 1600 9-9-9-24
      • Storage:
      • 256GB Samsung 840-Pro, 60GB OCZ Vertex 2, 1TB Seagate 7200.12, 1TB Seagate ES.2
      • Graphics card(s):
      • Gigabyte GTX 460 1GB SuperOverClocked
      • PSU:
      • NZXT Hale 90 750w
      • Case:
      • BitFenix Survivor + Bitfenix spectre LED fans, LG BluRay R/W optical drive
      • Operating System:
      • Windows 7 Professional
      • Monitor(s):
      • Dell U2311h 1920x1080
      • Internet:
      • 50Mb/s sadly gone, now on 3G dongle rubbish :(

    Re: LED Backlight flicker - common & dangerous?

    Reading the comments some folk say the newer revisions are supposed to have fixed the problem. To find out do what the guy has done - get a camera and film it. See what the playback looks like.

  3. #3
    Member
    Join Date
    Jun 2004
    Posts
    103
    Thanks
    0
    Thanked
    0 times in 0 posts

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by ik9000 View Post
    Reading the comments some folk say the newer revisions are supposed to have fixed the problem. To find out do what the guy has done - get a camera and film it. See what the playback looks like.
    To clarify I don't have the monitor that is on the video, but I have filmed my monitor (Viewsonic) through my phone camera and see the same lines that are on that video.

    Interestingly though if I turn the camera the lines go the other way. E.g. film with the phone held horizontally and lines go down the screen, if I hold the camera sideways the lines go sideways and if I hold it diagonally the lines, yep, go diagonally.

    Would be interesting if a few other people can try this out and see what happens..

  4. #4
    Senior Member
    Join Date
    Nov 2009
    Posts
    2,231
    Thanks
    578
    Thanked
    226 times in 184 posts
    • ik9000's system
      • Motherboard:
      • Asus P7H55-M/USB3
      • CPU:
      • i3-540, Prolimatech Megahalems, Akasa Apache 120mm
      • Memory:
      • 4x2GB Corsair XMS3 1600 9-9-9-24
      • Storage:
      • 256GB Samsung 840-Pro, 60GB OCZ Vertex 2, 1TB Seagate 7200.12, 1TB Seagate ES.2
      • Graphics card(s):
      • Gigabyte GTX 460 1GB SuperOverClocked
      • PSU:
      • NZXT Hale 90 750w
      • Case:
      • BitFenix Survivor + Bitfenix spectre LED fans, LG BluRay R/W optical drive
      • Operating System:
      • Windows 7 Professional
      • Monitor(s):
      • Dell U2311h 1920x1080
      • Internet:
      • 50Mb/s sadly gone, now on 3G dongle rubbish :(

    Re: LED Backlight flicker - common & dangerous?

    I pinged the guys at TFTCentral.co.uk an email and they gave the following reply:

    Quote Originally Posted by TFTCentral.co.uk;
    Thanks for the email. We have a full article about the situation which you can read here: http://www.tftcentral.co.uk/articles...modulation.htm

    and we have tested for backlight flickering caused by PWM ever since in all our reviews See the “panel” section of the reviews since Feb 12
    so you might find your monitor is reviewed and their findings re this behaviour.

    And with the lines changing with orientation of your camera - I wonder if you're getting an effect of the capture rate + screen refresh of the camera itself. Others more in the know will be able to assist further I'm sure <bows out and wishes he knew more about these things>

  5. #5
    Member
    Join Date
    Jun 2004
    Posts
    103
    Thanks
    0
    Thanked
    0 times in 0 posts

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by ik9000 View Post
    I pinged the guys at TFTCentral.co.uk an email and they gave the following reply:



    so you might find your monitor is reviewed and their findings re this behaviour.

    And with the lines changing with orientation of your camera - I wonder if you're getting an effect of the capture rate + screen refresh of the camera itself. Others more in the know will be able to assist further I'm sure <bows out and wishes he knew more about these things>
    Thanks for this.

    I've fired them a quick email as they don't have a review of my monitor, hopefully they don't mind.

    I've requested a return which has been accepted by the seller.

    I'm just not sure what to do. Its a shame as it seems a decent monitor. The only way I'd know if it caused any problems to me would be to use it for a while which may cause problems should I want to return it.

    TBH was expecting a few people to tell me theres no danger when I posted this but it doesn't' seem very active in here!

  6. #6
    mutantbass head Lee @ SCAN's Avatar
    Join Date
    Dec 2003
    Location
    M28, Manchester
    Posts
    13,975
    Thanks
    329
    Thanked
    627 times in 543 posts
    • Lee @ SCAN's system
      • Motherboard:
      • Asus P8Z68V Pro
      • CPU:
      • Intel I5 2500K & Corsair H100i Cooler @ 4.5-5 GHz
      • Memory:
      • 8 GB Corsair Vengeance 1600 Mhz 'Arctic white' 1.35V
      • Storage:
      • 4 x 250GB Samsung 840 EVO
      • Graphics card(s):
      • MSI GTX 770 Gaming Edition
      • PSU:
      • Antec Truepower 750W Modular Blue
      • Case:
      • Corsair 600T White Edition
      • Operating System:
      • Windows 8.1 PRO + MCE
      • Monitor(s):
      • 27" Asus MX279H & 24" Acer 3D GD245HQ + the 3D glasses
      • Internet:
      • BT Infinity

    Re: LED Backlight flicker - common & dangerous?

    Do you notice any flicker when not looking through a camera or a phone?

    If not, its nothing to worry about - all LED flickers, just so fast your eyes can't detect the changes.

  7. #7
    Senior Member
    Join Date
    Nov 2009
    Posts
    2,231
    Thanks
    578
    Thanked
    226 times in 184 posts
    • ik9000's system
      • Motherboard:
      • Asus P7H55-M/USB3
      • CPU:
      • i3-540, Prolimatech Megahalems, Akasa Apache 120mm
      • Memory:
      • 4x2GB Corsair XMS3 1600 9-9-9-24
      • Storage:
      • 256GB Samsung 840-Pro, 60GB OCZ Vertex 2, 1TB Seagate 7200.12, 1TB Seagate ES.2
      • Graphics card(s):
      • Gigabyte GTX 460 1GB SuperOverClocked
      • PSU:
      • NZXT Hale 90 750w
      • Case:
      • BitFenix Survivor + Bitfenix spectre LED fans, LG BluRay R/W optical drive
      • Operating System:
      • Windows 7 Professional
      • Monitor(s):
      • Dell U2311h 1920x1080
      • Internet:
      • 50Mb/s sadly gone, now on 3G dongle rubbish :(

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by Lee @ SCAN View Post
    Do you notice any flicker when not looking through a camera or a phone?

    If not, its nothing to worry about - all LED flickers, just so fast your eyes can't detect the changes.
    I would agree with this - if you can use it for a long period and your eyes don't hurt reading text documents and watching playback then it's probably all good.

  8. #8
    Senior Member Pob255's Avatar
    Join Date
    Apr 2007
    Location
    London
    Posts
    9,426
    Thanks
    491
    Thanked
    1,112 times in 1,027 posts
    • Pob255's system
      • Motherboard:
      • Asus M5A99X EVO
      • CPU:
      • PhenomII x4 955 & CM Hyper 212+
      • Memory:
      • 2x 4gb Corsair Vengence 1600mhz cas9
      • Storage:
      • 250gb SATA Westerndigital + 500gb samsung +1tb Samsung
      • Graphics card(s):
      • Asus GTX560ti CuII
      • PSU:
      • Be Quiet E9 680w
      • Case:
      • HAF 912+
      • Operating System:
      • W7 Pro
      • Monitor(s):
      • Acer P223w 22" TFT DVI

    Re: LED Backlight flicker - common & dangerous?

    There's one thing that article doesn't cover is that this has been deliberately used by a few manufactures to increase the response times.

    Pob's new mod, Soviet Pob Propaganda style Laptop.
    "Are you suggesting that I can't punch an entire dimension into submission?" - Flying squirrel - The Red Panda Adventures

  9. #9
    Senior Member kalniel's Avatar
    Join Date
    Aug 2005
    Posts
    24,111
    Thanks
    913
    Thanked
    2,163 times in 1,768 posts
    • kalniel's system
      • Motherboard:
      • Gigabyte X58A UD3R rev 2
      • CPU:
      • Intel i7 950
      • Memory:
      • 12gb DDR3 2000
      • Graphics card(s):
      • AMD HD7870
      • PSU:
      • XFX Pro 650W
      • Case:
      • Cooler Master HAF 912
      • Operating System:
      • Win 7 Pro x64
      • Monitor(s):
      • Dell U2311H
      • Internet:
      • O2 8mbps

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by Pob255 View Post
    There's one thing that article doesn't cover is that this has been deliberately used by a few manufactures to increase the response times.
    Or decrease perceived response times Like black frame insertion.

  10. #10
    Senior Member
    Join Date
    Nov 2009
    Posts
    2,231
    Thanks
    578
    Thanked
    226 times in 184 posts
    • ik9000's system
      • Motherboard:
      • Asus P7H55-M/USB3
      • CPU:
      • i3-540, Prolimatech Megahalems, Akasa Apache 120mm
      • Memory:
      • 4x2GB Corsair XMS3 1600 9-9-9-24
      • Storage:
      • 256GB Samsung 840-Pro, 60GB OCZ Vertex 2, 1TB Seagate 7200.12, 1TB Seagate ES.2
      • Graphics card(s):
      • Gigabyte GTX 460 1GB SuperOverClocked
      • PSU:
      • NZXT Hale 90 750w
      • Case:
      • BitFenix Survivor + Bitfenix spectre LED fans, LG BluRay R/W optical drive
      • Operating System:
      • Windows 7 Professional
      • Monitor(s):
      • Dell U2311h 1920x1080
      • Internet:
      • 50Mb/s sadly gone, now on 3G dongle rubbish :(

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by kalniel View Post
    Or decrease perceived response times Like black frame insertion.
    sounds painful! Like one of those embarrassing medical tales my Doctor friends tell me about....

  11. Received thanks from:

    kalniel (26-04-2013)

  12. #11
    Admin Team peterb's Avatar
    Join Date
    Aug 2005
    Location
    Southampton
    Posts
    12,813
    Thanks
    1,311
    Thanked
    1,845 times in 1,487 posts
    • peterb's system
      • Motherboard:
      • Nascom 2
      • CPU:
      • Z80B
      • Memory:
      • 48K 8 bit memory on separate card
      • Storage:
      • Audio cassette tape - home built 5.25" floppy drive
      • Graphics card(s):
      • text output (composite video)
      • PSU:
      • Home built
      • Case:
      • Home built
      • Operating System:
      • Nas-sys
      • Monitor(s):
      • 12" monocrome composite video input
      • Internet:
      • No networking capability on this machine

    Re: LED Backlight flicker - common & dangerous?

    Most lights powered from an AC power source exhibit flicker to a greater or lesser degree. In the UK it will be flicker at 100Hz. However the eye/brain does not consciously detect flicker above around 25Hz, although fluorescent tubes can sometimes be seen to flicker if they are looked at from the edge of the eye as peripheral vision is more sensitive to movement (which in effect is what flicker is)

    In incandescent lighting, the thermal lag of the filament smooths out the pulses of light, and in older CRT televisions which had a flicker 25Hz, longer persistence phosphors achieved the same effect.

    If you can visible detect flicker in a monitor, then it should be rejected, but if you can't (and all monitors are switching pixels on and off) then I doubt it is anything to worry about.
    (\__/)
    (='.'=)
    (")_(")

    My broadband speed - 750 Meganibbles/minute

  13. #12
    root Member DanceswithUnix's Avatar
    Join Date
    Jan 2006
    Location
    /dev/boogie
    Posts
    3,741
    Thanks
    90
    Thanked
    285 times in 259 posts
    • DanceswithUnix's system
      • Motherboard:
      • M5A-97 EVO R2.0
      • CPU:
      • FX-8350
      • Memory:
      • 2x4GB Ballistix Sport 1600
      • Storage:
      • 660GB Linux, 250GB Games (Win 7)
      • Graphics card(s):
      • Palit 460GTX 2GB
      • PSU:
      • 650W Corsair TX
      • Case:
      • Antec 300
      • Operating System:
      • Fedora 19 + Win 7 Pro 64
      • Monitor(s):
      • Samsung 2343BW 2048x1152 23" lcd
      • Internet:
      • 40Mb VDSL

    Re: LED Backlight flicker - common & dangerous?

    The bit in that article about using a linear voltage to drive the LEDs is I think fantasy, it would make the monitor less efficient, less reliable and harder to manufacture (hence more expensive) so people wouldn't buy it. Trying to get an even light across all the LEDs around the display would be a nightmare. I suspect that macbook they site as being linear is actually just driving the pwm at something like 10KHz. That would require some care in the driving circuit, at least not to start radiating radio emissions like crazy, but should be relatively easy.

    I have worked with cheap consumer displays in the past which were all LED backlit (on a small monochrome display it is easy and cheap). I used error diffusion techniques to drive the backlight, so that camera trick would produce some very funky patterns on one of my displays I did that because at very low brightness levels I didn't like the simple PWM output, at normal levels I just couldn't see it though.

  14. #13
    Senior Member
    Join Date
    Nov 2009
    Posts
    2,231
    Thanks
    578
    Thanked
    226 times in 184 posts
    • ik9000's system
      • Motherboard:
      • Asus P7H55-M/USB3
      • CPU:
      • i3-540, Prolimatech Megahalems, Akasa Apache 120mm
      • Memory:
      • 4x2GB Corsair XMS3 1600 9-9-9-24
      • Storage:
      • 256GB Samsung 840-Pro, 60GB OCZ Vertex 2, 1TB Seagate 7200.12, 1TB Seagate ES.2
      • Graphics card(s):
      • Gigabyte GTX 460 1GB SuperOverClocked
      • PSU:
      • NZXT Hale 90 750w
      • Case:
      • BitFenix Survivor + Bitfenix spectre LED fans, LG BluRay R/W optical drive
      • Operating System:
      • Windows 7 Professional
      • Monitor(s):
      • Dell U2311h 1920x1080
      • Internet:
      • 50Mb/s sadly gone, now on 3G dongle rubbish :(

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by peterb View Post
    Most lights powered from an AC power source exhibit flicker to a greater or lesser degree. In the UK it will be flicker at 100Hz. However the eye/brain does not consciously detect flicker above around 25Hz, although fluorescent tubes can sometimes be seen to flicker if they are looked at from the edge of the eye as peripheral vision is more sensitive to movement (which in effect is what flicker is)

    In incandescent lighting, the thermal lag of the filament smooths out the pulses of light, and in older CRT televisions which had a flicker 25Hz, longer persistence phosphors achieved the same effect.

    If you can visible detect flicker in a monitor, then it should be rejected, but if you can't (and all monitors are switching pixels on and off) then I doubt it is anything to worry about.
    The TFTCentral article linked above discusses this 25Hz thing- it's not actually true. We can see much higher frequencies, and not just peripherally. I thought the threshold for non-peripheral was circa 50Hz and peripheral can detect even higher.

  15. #14
    root Member DanceswithUnix's Avatar
    Join Date
    Jan 2006
    Location
    /dev/boogie
    Posts
    3,741
    Thanks
    90
    Thanked
    285 times in 259 posts
    • DanceswithUnix's system
      • Motherboard:
      • M5A-97 EVO R2.0
      • CPU:
      • FX-8350
      • Memory:
      • 2x4GB Ballistix Sport 1600
      • Storage:
      • 660GB Linux, 250GB Games (Win 7)
      • Graphics card(s):
      • Palit 460GTX 2GB
      • PSU:
      • 650W Corsair TX
      • Case:
      • Antec 300
      • Operating System:
      • Fedora 19 + Win 7 Pro 64
      • Monitor(s):
      • Samsung 2343BW 2048x1152 23" lcd
      • Internet:
      • 40Mb VDSL

    Re: LED Backlight flicker - common & dangerous?

    Quote Originally Posted by ik9000 View Post
    The TFTCentral article linked above discusses this 25Hz thing- it's not actually true. We can see much higher frequencies, and not just peripherally. I thought the threshold for non-peripheral was circa 50Hz and peripheral can detect even higher.
    It is a very personal thing. I think my threshold is slightly lower, as I have always been able to tolerate cheap CRT monitor flicker with ease. Others have told me they couldn't stand CRTs below 75Hz, and I have to believe them.

  16. #15
    Senior Member Pob255's Avatar
    Join Date
    Apr 2007
    Location
    London
    Posts
    9,426
    Thanks
    491
    Thanked
    1,112 times in 1,027 posts
    • Pob255's system
      • Motherboard:
      • Asus M5A99X EVO
      • CPU:
      • PhenomII x4 955 & CM Hyper 212+
      • Memory:
      • 2x 4gb Corsair Vengence 1600mhz cas9
      • Storage:
      • 250gb SATA Westerndigital + 500gb samsung +1tb Samsung
      • Graphics card(s):
      • Asus GTX560ti CuII
      • PSU:
      • Be Quiet E9 680w
      • Case:
      • HAF 912+
      • Operating System:
      • W7 Pro
      • Monitor(s):
      • Acer P223w 22" TFT DVI

    Re: LED Backlight flicker - common & dangerous?

    On CRT's it wasn't just about consciously perceived flicker it was about the autonomic perceived flicker.
    ie you don't "see" the flicker but your eyes and nervous system do pick it up.
    In my case a 60hz CRT wouldn't look like it was flickering but would trigger headaches after extended periods, up the rate to 75hz and the headaches wouldn't occur.
    CRT was a different effect because it was a complete top to bottom single pass of the electron beam, yes tft screens do a single pass as well but it's a change state pass of the lcd matrix, not a phosphor luminescence trigger of scanning electron beam.

    As to flicker generated by AC current, the problem is that while a monitor is powered by AC current the panel is not, it's powered by DC, a monitor has a power board in it (or a separate power brick) to rectify the AC into DC.
    By reducing the voltage to the back light LED's you could reduce the brightness of them in a flat manner, but the range of brightnesses is not a great and dynamic control is far more complex to achieve than it is by PWM control.

    Pob's new mod, Soviet Pob Propaganda style Laptop.
    "Are you suggesting that I can't punch an entire dimension into submission?" - Flying squirrel - The Red Panda Adventures

  17. #16
    root Member DanceswithUnix's Avatar
    Join Date
    Jan 2006
    Location
    /dev/boogie
    Posts
    3,741
    Thanks
    90
    Thanked
    285 times in 259 posts
    • DanceswithUnix's system
      • Motherboard:
      • M5A-97 EVO R2.0
      • CPU:
      • FX-8350
      • Memory:
      • 2x4GB Ballistix Sport 1600
      • Storage:
      • 660GB Linux, 250GB Games (Win 7)
      • Graphics card(s):
      • Palit 460GTX 2GB
      • PSU:
      • 650W Corsair TX
      • Case:
      • Antec 300
      • Operating System:
      • Fedora 19 + Win 7 Pro 64
      • Monitor(s):
      • Samsung 2343BW 2048x1152 23" lcd
      • Internet:
      • 40Mb VDSL

    Re: LED Backlight flicker - common & dangerous?

    The links here were about the panel being uncomfortable to use rather than actually seeing flicker, so sounds like much the same thing. As I said, I am not that sensitive to flicker (or headlamps at night, possibly related?) hence my comment that this is a personal thing which you can't read off a review unless you have calibrated your own tolerence somehow.

    Sadly the money I save on cheap monitors has to go into expensive speakers, even in my 40's I seem to have quite a high frequency range of hearing and can't tolerate sloppy speaker design

    My point with voltage controlling LEDs is that each LED will respond differently to a given current, each one will have a slightly different turn on voltage. So each LED would require its own regulator transistor at least, and even then you would probably have to do some sort of binning of the devices to get matched sets of diodes. Nah, just turn them on and off. If it flickers, turn them on and off faster.

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •