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Thread: LCD problem

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    LCD problem

    Well, actually the problem is with a client who bought a new Samsung 931BW LCD monitor from me. She is complaining it is giving her headaches and she also suffers from nausea if she sits in front of it for more than 10 minutes. I have this exact same monitor in another room which is part of a new system I built for another client and I have sat in front of it for hours and haven't experienced any such problem(s).

    Is this complaint something unusual?

    Is there something that could be done to rectify the problem?

    Jeff
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    Re: LCD problem

    Make sure the refresh rate is set to that recommended bt Samsung.

    Joe
    Joe

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    Re: LCD problem

    Joe,

    There is no "recommended" refresh rate. But it does have two options available in the Display Settings...... 60 Hz or 75 Hz and I set it to 75 Hz which many recommend as being best. Yes? No?

    Jeff
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    Re: LCD problem

    You could try setting it to 60 Hz to see if the client likes that better.

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    Re: LCD problem

    ....and on a non-technical answer, get her to go for a medical check up and eye test, just on the safe side
    Jerry

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    Re: LCD problem

    Whatever you do, it would be a good idea to make sure she SEES you make a change. I'm not being a smart aleck when I suggest: might this be a psychosomatic problem? If adjusting a setting (refresh or whatever) doesn't immediately clear it up, I'd get that monitor out of there quickly.

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    Re: LCD problem

    I thought that the conventional wisdom on flat panel/LCD/TFT monitors was that (unlike for CRTs) the refresh rate was largely irrelevant?

    The lady concerned does not suffer from epilepsy, or any other such problem with flickering lights? It would be surprising if she didn't have problems with the house lighting, TVs, etc, if that was the case.

    John
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    Re: LCD problem

    I believe the higher the refresh rate the better and the other thing to check is the 'ClearType' setting.

    It may also be worth playing around with ambient lighting. If the main lighting is fluorescent, check they have CAT3 diffusers (I think that's what is required) and sometimes a small incandescent desk lamp can help to over-ride ambient flicker.

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    Re: LCD problem

    Just found the link to the MS page on ClearType. You may need to run it under IE, and it wants to install an ActiveX control thingy...

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    Re: LCD problem

    Jeff,

    <hr>Is this complaint something unusual?<hr>
    In a word, YES, at least with a normal functioning LC monitor. Your problem may well be with your client and not the monitor.

    What you have to do is to literally see what her monitor is doing. The fact that you have a similar monitor with no problems is of no consequence. When you look at her monitor check for any image swimming, jerking, scrolling or pulsing. If you notice anything of that nature, even it is minor to you and bothers you none, then switch the monitor out. If the problem is still there with monitor 2 then check the video subsystem of the computer.

    There are many reports of people having problems with monitors, but not one that I am aware of where only the operator can see the problem. Usually a problem affecting an operator can be seen by others and most of the other viewers have no problem with the stimulus. The vast majority of such problems are associated with CRTs. Some items that users have issues with are luminance (too bright or too dim), non stable character placement on the screen, low contrast, fuzzy characters and bad placement of monitor ( operator has a window with sun coming in behind the monitor and perhaps has down, but open, blinds ) and flicker.

    Flicker should not be the problem if the monitor is functioning normally - period! You should know, however, that there is a wide range of flicker sensitivity in people. In the industry we had people who were "flicker lookers" and they were used to check out new monitor designs. If they could see no flicker, the design passed. Flicker lookers were typically young and female. If you want to check for flicker that may be faint to you, darken the room and put up an all white (or mostly white) screen and run up the luminance.

    Let me know what you find.

    Paul

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    Re: LCD problem

    Thanks to all for your replies. I am in full agreement with what has been said. <img src=/S/grin.gif border=0 alt=grin width=15 height=15>

    Re: "ClearType"... that too is something I automatically install with a LCD monitor; ClearType Tuner, part of Microsoft's "PowerToys". In fact, I ran the ClearType Tuner Wizard at least 3 times with this woman letting her choose which configuration she was most comfortable with.

    It has been my understanding also that "flicker" mostly applies to CRT monitors which are used in an environment where flourescent lighting is present. This is not the case here since the monitor is an LCD and there is no flourescent lighting in the room. In fact, there is little lighting of any kind in the room other than one small incandescent table lamp and ambient light supplied through one window which is located on the backside of the monitor.

    Additionally, this woman is in her 60's, so the typical although she is female she doesn't qualify for the "young" criteria. <img src=/S/wink.gif border=0 alt=wink width=15 height=15> I have again recommended that she play with the brightness and contrast controls and to bring more artificial lighting into the room. I suspect, however, that none of these suggetions are going to remedy the situation..... just a feeling. <IMG SRC=http://www.the-highway.com/Smileys/scratchchin.gif>

    Jeff
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    Re: LCD problem

    Jeff,
    <hr>It has been my understanding also that "flicker" mostly applies to CRT monitors which are used in an environment where flourescent lighting is present<hr>
    Not exactly. Flicker is a general phenomenon that might come from any time varying light source. It is the perception that the light is not steady or that it pulsates. The response to flicker can range from simply noticing it to serious neurological problems (in rare instances and under special circumstances). Most people find flicker to be something they want to have go away.

    The primary parameters of a light source that affects our perception of flicker are its repetition rate and the percentage modulation of that light signal. The human visual system time integrates light falling on the retina and produces a perception of some time-averaged luminance. If the repetition rate is high enough (compared to the integration time constant) only a steady light level is perceived. As the rep rate is lowered we begin to notice light pulsation or flicker. Under fixed conditions an individual will perceive only a steady light at and above their critical fusion frequency (CFF). Perception of flicker increases as the rep rate decreases below the CFF and increases as the modulation percentage increases.

    So as CRTs produce a burst of light at a pixel when hit by its electron beam and decays rapidly thereafter until hit again by the beam at the refresh rate, the light reaching our retina is highly modulated and if the refresh rate is less than about 75 Hz a majority of people will see flicker. So whether there are fluorescent lights in the room, or incandescents or open flame torches that has only a secondary effect on perceiving flicker from a display.

    An LCD pixel on the other hand produces (actually it simply transmits) an almost steady light, that is, a light that has a large dc component and a small modulation at the refresh rate. For this type light source the CFF can be much lower so setting an LC monitor to 75 HZ or 60 HZ (or even less on well designed monitors) usually produces no perceived flicker. Display electronics failure, however, can can change the LCD behavior such that it not only has higher modulation, but also a light frequency component at half the refresh rate - when this happens flicker can be VERY evident on an LC monitor.

    Paul

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    Re: LCD problem

    Paul,
    First of all, I want to say that I'm NOT trying to be impolite or negative, please understand that.

    I DO agree with your post and it's rather detailed contents. With my engineering background, I can understand just what you are saying.

    However, perhaps you should lighten up your explanations by omitting a lot of the scientific information and stating it in a more everyday language?

    Again, please understand what I am saying here. Don't take it wrong, neighbor.
    BOB
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    Re: LCD problem

    Bob,
    I will accept your comments as constructive criticism. The subject you raise deserves some response, however.

    Flicker is a complicated topic. There have been over a thousand studies on flicker in the human visual system and several times that number of papers. It is no wonder that it is not universally understood even in the technical community. Having reread what I wrote I make no apologies for the content of the posting or its style. I distilled a LOT of information into three small paragraphs containing the essence - a general effect with time varying light sources, rate dependent and modulation dependent. The nearest I felt I came to missing some of our audience was with the term modulation. It is a concise and precise term so I left it in and expected that if someone was interested in flicker and was not familiar with the term that they would post a query, which I would be glad to answer.

    I think there is a time and place for precise answers and I felt my posting was appropriate on both counts. Since you understood what I wrote and think it is accurate, I will take that as a positive response from you. As for others on the forum, I feel it is up to those who did not understand the post, or who think it is incorrect in some way to let me know, as they have a legitimate beef with my posting - and I welcome such input.

    Paul

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    Re: LCD problem

    For what it's worth, although I am NOT an engineer, I think I understood your posts quite well and they were brief enough as to be easily readable. I think you should "keep on truckin' " Paul. Even modulation is not so heavy a topic that I can't get my arms around it. Thanks for the input.

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