Migraine headaches from LED backlighting in x200t

Discussion in 'Lenovo (IBM)' started by Cirrus, Dec 3, 2008.

  1. Cirrus

    Cirrus Pen Pal - Newbie

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    Hey everyone,
    I was just wondering if anyone has experienced any problems with their x200t tablet with regards to the backlighting. I have found that I am sensitive to LED backlighting in computers and would like to know if anyone else has experienced the same thing. The x200t seems like a very nice tablet PC but if it gives others the same problems as me then thats just a deal breaker for me.
     
  2. Grimnir

    Grimnir Think tank & Designer Senior Member

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    Why is it not a deal breaker if it gives YOU the problem vs everyone else?

    I'd think that LED backlighting would be better for you since its an even spread of light...odd. Have you tried viewing the machine with lower light intensity settings? Are you sure its the backlight and not just the monitor itself? Ie do you have glasses/need glasses/have something like epilepsy?

    It could be the digitizer on the tablet pc...it can sometimes make the screen look grainy or like a grid which could agitate things like epilepsy if you happen to have it.

    Not trying to scare you or anything or say that its all you , but those are just some suggestions.
     
  3. TabbedOut

    TabbedOut Scribbler - Standard Member Senior Member

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    I would have thought one would be more sensative to a CCFL backlight vs an LED one due to the flicker of the flourescent bulb vs the constant light from an LED... but really it is what triggers YOUR migraines. All that you would get in a forum like this is anecdotal evidence, and does that matter really if YOU are uncomfortable? I would never purchase a computer that hurt me, but to each his/her own I suppose.

    [​IMG]
     
  4. makito

    makito Since 2006? wow...

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    Trouble with LED back lighting is how they dim the screens - They use something like PWM, basically flickering the LED back lights on and off - increasing the time it's off to make it appear dimmer. It's simpler and more efficient to vary the light output this way than to do it like a typical light dimmer.

    The down side is in fact yes, the back light can cause headaches because while you may not be able to see it, it is flickering. A quick way to check - go into a dark room and turn up the screen brightness to 100%. Wave your hand infront of the screen; then repeat with the screen turned down all the way. You'll see a similar effect as waving your hand infront of a strobe light or your old style tube-TV.

    What can you do about it? Not a whole lot - it's how it works, but there are two tips:
    1. Keep the brightness at 100% always to minimize flicker.
    2. If it the screen is too bright at 100%, wear sunglasses (I know, it's dorky)
     
  5. makito

    makito Since 2006? wow...

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    Ooh as an addendum - why isn't this a problem or as big as a problem on standard CCFL back lit screens? CCFLs employ higher switching frequencies. Microsemi, a manufacturer of inverters for CCFL back lights runs at 68+Khz. Typically you can't even perceive any difference after 60-120hz.
     
  6. schmolch

    schmolch Scribbler - Standard Member

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    How did you come to this conclusion?
    I have a few LED Lights in my room and they are more comfortable to me than any other Light i have (CFLs and FLs).
     
  7. Frank

    Frank Scribbler - Standard Member Senior Member

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    @makito:
    Your description is not possible. The PWM frequency shouldn't cause flicker or headaches at all. But I admit, that I don't know the exact frequency.

    Second: The frequency is constant, regardless if bright or dim, that's why it is called Pulse-width modulation, it only varies the width of the pulse.
    So the frequency stays the the same.


    The headaches can come from the smaller font on the 12" display, bad ergonomic position of the display, maybe you always have to look down, I don't know your setup, glossy display and the reflections, too bright, too dark.
    But it's not the LED backlight.
     
  8. makito

    makito Since 2006? wow...

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    Hehe I stand corrected on my terminology - yes PWM uses a fixed frequency but it's the pulse width that essentially gives he same effectas lowered effective frequency.Well what I really mean is, regardless there is a off time and an on time for the led back lights that he maybe sensitive to.

    Either way would certainly say - don't purchase a computer that doens't agree with your body. you can replace a computer but you can't replace your mind or eyes! Best of luck.

     
  9. LenovoGringo

    LenovoGringo Scribbler - Standard Member

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    Cirrus,

    If you are hesitant of getting an LED display, why don't you just order a X200 with CCFL backlighting????? I don't see the "deal-breaker" dilemma here.
     
  10. Frank

    Frank Scribbler - Standard Member Senior Member

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    just for completion:
    Thank you makito, who brought me to the idea to measure the PWM signal of my tablet PC with the help of an oscilloscope and a photo resistor.
    I used a photo transistor instead, had no photo resistor :p

    I measured the frequency of both my Fujitsu T2010 display as well as the display of a Sony VAIO TX2 notebook, both LED backlit.

    The periodic time is T=2ms and so the frequency f=500 Hz.

    The only funny thing was that the T2010 display always used a PWM signal to control the brightness whereas the TX2 disabled the PWM at full brightness.

    Cirrus asked about the Lenovo x200t. I don't have one :p, but I don't think that it will use a different frequency, because both the Sony and the Fujitsu use the same frequency, whereas both computers are totally different. I think 500Hz is a common used frequency. I don't know it, but I just can't believe that Lenovo uses a much lower frequency for their PWM.
     
  11. rock7777

    rock7777 Pen Pal - Newbie

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    I just discovered that my X200 Tablet with a Superbright LED display flickers when on battery - even at the highest brightness setting. The flicker stops when the tablet is plugged in and I set the brightness at the highest setting. Has anyone else noticed this?

    The flicker is not readily noticeable to the unaided eye. The tell-tale factor for me was the severe eyestrain i would experience whenever I use my X200t on battery. I don't have an instrument to measure the flicker rate of the screen but I can use my cell phone camera to detect the flicker. A cell phone camera usually has a very slow refresh rate (you can see pronounced motion blur on the display when you wave you phone around). Normally when you point the cell phone camera at a conventional LCD monitor (ccfl backlight), the resulting display on the cell phone is rock solid. But when you point the cell phone at a CRT monitor you will notice a series of vertical or horizontal bands that move in one direction across your cell phone display. This is due to the low frequency flicker that interferes with the refresh rate of your cell phone camera. My eyes are definitely a lot more relaxed when I'm plugged in with the display at full brightness despite the fact that it is almost blindingly bright.

    Can you guys try this with your X200 Tablet LED display? I've tried using my Samsung cell phone as well as someone else's iPhone. I get the same banding pattern on my x200 tablet at any brightness level when it is running on batteries. When the x200 tablet is plugged in, I get the banding pattern on all brightness level except for the highest brightness level.

    Can anyone confirm these results? Can anyone propose a solution for this?
     
  12. resonantworks

    resonantworks Dev

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    I don't get any extreme headaches (yet!) but I definitely noticed the flicker as soon as I turned on the X200. Fortunately I do have the equipment to measure this ;)

    The X200 tablet (LED + touch) LCD panel is pushing out a 90Hz PWM to drive the LEDs. When plugged in at full brightness the LEDs are driven 100% of the time, so no flicker. When on battery the LEDs are driven at around 90% of the time. This was measured at max brightness in both cases.

    I keep the machine plugged in and at max brightness to overcome this issue, but yes it is quite bright indoors unfortunately.

    Here in the UK we get only one model (LED+touch) so even if we wanted to get the CCFL based screen we can't!
     
  13. rock7777

    rock7777 Pen Pal - Newbie

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    Thanks resonantworks. I'm surprised that the LCD panel can only push out 90 Hz when it's plugged in and at maximum brightness. I would have expected a much higher frequency. I wish there was some way to keep the higher frequency when on battery. Again, I'm willing to sacrifice some battery life for eye strain/headache relief. I'm hoping LED backlit screens do not become even more pervasive - this is definitely my last LED backlit laptop I purchase unless the technology improves.
     
  14. Kyle Porter

    Kyle Porter Veteran Moderator Senior Member

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    I find it interesting people are having this issue. I had a similar issue to this with my 2710p, but it turns out i had eye troubles and needed glasses :S
     
  15. Frank

    Frank Scribbler - Standard Member Senior Member

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    but 90Hz is really low.
    Fujitsu uses 500Hz, which is a reasonable frequency.

    I know some people who can see 90Hz flicker on CRT monitors without a problem. And I also think that I might get disturbed with such a low frequency, especially at the edges of the field of view of my eyes I also see flickering of CRT monitors which run with a frequency around 90Hz.

    So 90Hz is too low and other manufacturers like Sony and Fujitsu know this and use a higher frequency.
     
  16. resonantworks

    resonantworks Dev

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    One possible trick you can use to overcome the brightness (when using at max to overcome flicker) is to use custom colour profiles in the intel driver (on Vista). I'm using 3 profiles at the moment. One colour corrected using the full range, one with the brightness setting all the way down and another with the both the brightness and contrast setting all the way down.

    To get to this control panel in Vista:
    1. Right click desktop -> Personalize
    2. Display Settings
    3. Advanced Settings
    4. "Intel (R) Graphics ..."
    5. Graphics Properties
    6. Color Correction

    These are my current "schemes"...
    "Colour corrected":
    Red: gamma = 1.3, brightness = 0, contrast = 50
    Grn: gamma = 1.2, brightness = 0, contrast = 50
    Blu: gamma = 1.1, brightness = 0, contrast = 50

    "Medium":
    Red: gamma = 1.3, brightness = -60, contrast = 50
    Grn: gamma = 1.2, brightness = -60, contrast = 50
    Blu: gamma = 1.1, brightness = -60, contrast = 50

    "Low":
    Red: gamma = 1.3, brightness = -60, contrast = 40
    Grn: gamma = 1.1, brightness = -60, contrast = 40
    Blu: gamma = 1.0, brightness = -60, contrast = 40

    This 'trick' does cripple the screen from displaying the full gamut, but if you are just text editing (or programming) in a subdued light setting then it might be easier than fetching the sunglasses or putting some 'smoky grey acetate' sheets over the screen :)
     
  17. rock7777

    rock7777 Pen Pal - Newbie

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    Can anyone else confirm flicker on your LED backlit laptop using your cell phone? Just point your cell phone camera at your laptop screen and see if you can see a horizontal or vertical banding pattern that moves across the screen (when viewed through your cell phone display). Try this at various brightness levels plugged and unplugged. Does the flicker bother anyone, i.e. eye strain/headaches?

    Again I have flicker 100% of the time when unplugged (regardless of brightness level). When I'm plugged in, I get detectable flicker on all brightness levels except at the highest level. This is disappointing because a big selling point of my laptop was its long battery life. Now, for the sake of my eyes and sanity, I find myself seeking an outlet no matter how much battery life is left on my laptop.
     
  18. resonantworks

    resonantworks Dev

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    I've read somewhere that another manufacturer updated their bios to have the screen on full (no flicker) when set to max brightness when on battery mode. Unlikely that Lenovo would be moved to do this (I'm still waiting for the HP-like fn-ctrl swap in bios) you might have more luck trying on the official Lenovo forums:
    http://forums.lenovo.com/lnv/board?board.id=X_Series_Tablet_ThinkPads

    If that fails you could try get Lenovo to refit the screen with the CCFL display due to 'health reasons' or a possibly even a full refund?

    90Hz is way too low. This same issue happened (still happening?) on the MacBook Pro line. I don't understand which troop of morons allowed this without the proper field testing.

    Yes, most CRT monitors are flicker-free at 60Hz or 75Hz, but then they use different technology altogether. The phosphor fades away 'slowly' reaching 0-50% brightness by the next refresh where it gets pumped back up to 100%, so it never reaches 0% immediately. PWM on LEDs switch from 100% to 0% immediately producing a strobe effect.

    Best way to compare is to think of CRTs as halogen lamps and LED backlit LCDs as disco strobes. Now imagine turning them on and off repeatedly with a switch - you get the picture ;)

    (And CCFL LCDs switch at a very high frequency - so no issue there for most mammals!)
     
  19. rock7777

    rock7777 Pen Pal - Newbie

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    resonantworks, thanks again for your input. It is a very annoying issues. I was really excited about LED displays - they were so heavily touted for their efficiency, brightness, and longevity (they don't fade over time like CCFL's). No one told me about the flickering issue. I thought the days of flickering displays were gone with the popularity of LCD screens. With CRT monitors, I was immediately able to detect flicker at 60 Hz but at 75Hz and beyond, my eyes would begin to relax. Like you describe, I think its something to do with low duty-cycle (the display's persistence) in LED displays along with a relatively low PWM of 90 Hz or lower that is wreaking havoc on my eyes.

    I think it will be a good idea to post this on the official Lenovo boards. I will keep you posted.
     
  20. resonantworks

    resonantworks Dev

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