LCDs with persistent images - BeHardware
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Written by Vincent Alzieu

Published on April 3, 2006

URL: http://www.behardware.com/art/lire/615/

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The overdrive donwside: LCDs burn in

One day you discover on your monitor an image that canīt be erased…
We regularly play the roll of the bearer of bad news concerning LCDs. Lately you have already seen:
-14% tax on DVI (only Europe)
- absence of HDCP certification for almost all displays on the market;
- Mura effect on panels and backlight spots
- problems of color quality with time
- flagrant lack of brightness homogeneity in big monitors
All this is without recalling the recurrent problem of dead pixels.
If this wasnīt enough, here is something as interesting: the persistence of images on LCDs, which isnīt often covered by warranties.

We are not trying to shoot down LCD monitors to praise other alternatives, existing or future technologies. It’s more that with monitor tests, we progressively increase our knowledge in this domain and we sometime discover hidden defects.

It all started with the LG L2300C
The bad news of the day is that some LCDs tend to keep a ghost image of fixed images that have been displayed a little too long. In fact this problem isnīt completely new, but up to today, it was so minimal that we couldnīt consider it as problematic. No one mentioned it because no one noticed it. Unfortunately, the situation is getting worst.

We really became aware of the problem while testing the LG L2300C (in French). This 23" monitor is sold at very low prices, less than 800€. Its panel is a TV panel and its resolution, 1366 x 768 pixels, isnīt really appropriate for office use.

One Friday night, we forgot to switch off the test monitor. In the background there was our electronic mail service software tool. Monday morning when we came back, we had the unpleasant surprise of seeing that it was superimposed over all our images and several hours later, it was still there. We called LG, who was very honest, something that we are not used to with manufacturers.

Our electronic messaging software is in superimposition on the grey of Photoshop.
In the middle of the image we can see Canonīs logo that was present in a mail that we received last Friday.

LG didnīt really test the monitor before sending it to us and they were unaware of this problem. They werenīt surprised, however, to hear of this defect and they admitted that their big monitors intended for public display were also subject to this type of phenomenon for a year now. According to them, it happened with the change of the panel generation in 2005. Feedback from Korea didn’t give them an explanation and most of all didn’t correct it. There is only one way to counter this problem; display a white image for hours and this is what they told us to do with the L2300C. We did this alternately between work periods and after the third day, the persisting image really started not to become unnoticeable.

The good news is that it isnīt an irremediable burn in which happens in some plasmas. According to LG, the problem only happens with fixed images. Liquid crystals locked in the cells have red, green and blue filters that would progressively get stuck. There will be within the same cell, a part of the liquid crystals that would correctly react to the desired image and others that would get stuck in the position of the image that was displayed for the longest time.

Displaying a white image would enable a passing of a maximum of light, hot (place your hand on the surface of your LCD) and melt the part that is solid.

If they already were aware of this problem, the fact that we encountered it on the L2300C bothered LG who thought that only public displays were affected by this problem. Seeing that it appeared on a monitor available in stores for the general public is all the more problematic that they donīt have a miracle solution to counter it. The proof of how much this concerned them is that the L2300C is almost impossible to find on the market today. Its lifetime would have been very short.



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After LG, Nec, Samsung and the others confirmed it

Nec and Samsung confirm and give more precision...
Following this edifying conversation, we turned to two other major actors for public displays, Nec and Samsung. There again, we have to say that they were really honest with straight answers. They confirmed this problem for public displays. This is something that most manufacturers have corroborated. They also precised some information that depending on the mass of information gathered, there isnīt one type of persistence but three.

The Image retention would be a phenomenon visible on some LCD TVs. These are very furtive persistent images that last a few milliseconds. You just have to change of scene for the image to disappear completely. To counter this problem, manufacturers would have introduced a function called "orbiting", which consists of constantly slightly moving the image a few pixels on the side and in height. Reducing the brightness would also diminish this phenomenon. We were unable to put our finger on the real cause of this problem. Anyway, the remedy is rather simple and the disturbance is very occasional.

More visible and disturbing, Sticking appears with the Overdrive. Because of the latest overamplificatons to reduce response time by a few milliseconds, cells wouldnīt be able to entirely evacuate their load. This would be the most common phenomenon at least for IPS and VA technologies. According to our manufacturers, the only method of removing defects would be to switch off the monitor during the same amount of time as the persistent image has been displayed.

The third type of persistence, that according to LG we could come across on the L2300C, is called Stained LCD. Only public displays are concerned, those that are intended to display commercial messages in stores for example. The liquid crystals get stuck and to remedy this, LGīs method consists in pushing the brightness and contrast to a maximum for several hours.

... but Conrac disproves, and told us to take hike

All monitor manufacturers nevertheless admit their limitations. Their solutions to remove persistent images aren’t perfect or ideal because with certain exceptions (see Asus below) they are incapable of explaining in detail the reasons for these defects and most of all to remove them. These are only remarks made on their practical use of "faulty" monitors. All say that only one actor of the LCD world would have the solution against persistent images: Conrac…

You probably never heard of them and this is normal. This manufacturer only installs very big monitors in public places. For example, they equipped the Paris airport and they would have confronted this problem two years ago on all their monitors installed and they were asked to find a solution. We contacted them with a simple a question as which technology of panel was concerned, or how did you remove images that appeared?

It was like talking to a wall. They didnīt want to indicate the technology that was concerned at that time, the one used today, or what they do to avoid the monitors to have these images. They say that their "know how" is protected by patents and donīt want to give their solutions to competitors who would only be too happy to re-conquer markets that they left because of this defect.

They only agreed to precise two points:
  • According to them the first problem for LCDs is called Sticking. It would be due to not only the Overdrive as from their point of view this is only one factor (which is still important). Switching off the monitor for a long period of time wouldn’t be enough. So what should we do? They refused to answer, or even give us new leads. Too bad for general users.

  • for the Stained LCD, and they didnīt confirm its existence, the effect of a white image wouldn’t be more than a black image as backlights are never shut down. They are always at full use except when the monitor is in stand by. It was impossible to have more information and it took us a dozen of phone calls. In the end we felt that we really started to become a annoying by asking so many questions on the subject.


    • Page 3
    Manufacturers' answers

    Manufacturer answers for when the problem shows up
    What we learned from the story is that manufacturers are starting to re-introduce screensavers on monitors. Open your instruction book (sometime electronic) and look for safety and warranty conditions – that you have to read in theory before plugging in your monitor. Here is what we found for a selection of monitors chosen randomly from our stock:




    In alphabetic order, we start with Acer who answered that this afterglow effect isnīt characteristic to their LCDs. It has always existed if it’s for CRT, Plasma, video projectors, video or digital cameras. This is the reason why all OS versions have a security with standard settings:
    - Dynamic screensaver after 10 minutes of non-use
    - Total stand-by after 20 minutes of non-use

    If these 2 parameters are deactivated by the user, display peripherals wonīt be able to resist small degradations (noticeable after several hours or even days spend with the same image).
    It is an inadequate use of the existing technology for all manufacturers.
    In this specific case, Acerīs warranty doesnīt come into play.
    Acerīs warranty will only work if this problem is reproduced on a different computer than the one used by the consumer and their services are able to see it.

    On the one hand, they clearly say that no, the warranty isn’t valid. On the other hand they also say that it sometimes could be. If the technical services notice the presence of a persistent image, they will replace the monitor. This of course, after several hours/days of being switched on.


    Appleīs instruction book does not mention this phenomenon. On the phone, they explained that that we had to switch off the monitor and if the image is still there, bring the monitor to one of Appleīs stores which will carry out tests and determine if there is a reason or not use the warrant.


    Asusī warranty doesn’t cover this problem of persistent images. However, they have a different approach than their competitors. Their next two monitors, the PW191 (19 inches whose release date is imminent) and the PW201 (awaited in June) wonīt include an overdrive. So, this is the reason why they donīt have to cover monitors for image persistence because the disappearance of this function would cancel all risks. FYI, the PW191 is a TN, the PW201 a VA. They both will have 8 ms response time.


    Monitor: Belinea 10 20 35W, P-MVA 8 ms panel

    At Belinea, the translation of the instruction book leads to a problem of interpretation. The one in German, the manufacturer original language, speaks of "Einbrennungen", for "burning" in English. And in the English book, they speak of "picture tube burn-in". We called them and they confirmed that the phenomenon of marking wasnīt covered by the warranty.


    Monitor: new Dell series, various panels.

    Dell recommends switching off the monitor when it isnīt in use or using the screensaver. We were unable to know if this defect is covered by the warranty.



    HPīs answer is the most surprising. Here is a copy. "HP doesnīt want to answer that question."



    Iiyama also gave us a short answer, but the answer is opposite to HPīs. Their warranty works.


    We had some difficulties finding answers with LG. On the one hand, there are instruction books that you can download from a dedicated website. We downloaded several documents including the L2300C’s. None mentioned this problem.

    We took the role of an individual user who would have come across this problem. We were told to run the monitor for a week with various images. After this period of time, if the persistent image was still there, warranty services told us to use our warranty and replace the monitor.

    A third official version from a LG representative. They told us that after verification, we can read from the manual the following sentence, “the warranty "maintenance on site" and "return to technical station" arenīt applied if the monitor”:
    - has a default of image due to marking

    We didnīt find this in our book.


    Monitor concerned: NEC all recent products (we donīt have old NEC monitors in the office), all technologies.

    There is a new function included in Necīs latest high-end monitors. For the last XX90UXi series, there is a hidden menu that allows the activation of the overdrive. By default it’s currently deactivated. We could have thought at first that this option would have reduced the noise in video but it isnīt the case. Wouldnīt it be to diminish the risks due to persistent images following the display of fixed images?


    Monitor concerned : Samsung SyncMaster 215TW, PVA 8 ms panel

    For Samsung, the case isnīt specified in the warranty conditions. They emphasize that this problem is exceptional and that no case of this type has been solved over the past four years. They told us that the SAV team has a certain discretion in considering when to replace the LCD after technical verification if the LCD is durably marked.
    There are no official rules but a technical expertise and a commercial "settlement".


    Monitor : VP930, P-MVA 8 ms panel
    .ViewSonic refuses to take charge of a monitor with persistent image. This is specified in the owner’s manual. However they say not to know how to get rid of this effect.


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    Conclusion

    Conclusion and show down
    Everyone (except for manufacturers) agree on the basic principle. The phenomenon of image persistence appeared or became problematic when the panel manufacturers accentuated the overdrive to accelerate liquid crystals’ rotation. It happened two years ago, with the change from 16 ms to 12 ms LCDs. All have acknowledged this defect and to counter this problem they recommend turning off the monitor for a long period of time, or displaying various images and using screensavers.

    We came across the problem and we advise you to follow their advice. Working with a previous image in the background is very annoying and you quickly tend to focus on it. We have warned you that only a few manufacturers make their warranty work if this problem arises.

    We can hardly blame them as this default isnīt due to one unit in particular but to the principle of recent panels. If you start over the same procedure on the new unit and display for several consecutive days the same image without shutting down your monitor, you might have the same problem. So manufacturers should clearly indicate in their manuals instruction or even on the packaging (so you canīt miss it) that their monitors arenīt conceived to display fixed images for long periods of time and that you have to use screensavers to avoid any marking risks.

    And then there is the discordant voice of Conrac, who builds public displays. They say to have discovered THE truth but donīt want to share the information. Too bad…

    However, to put the danger in perspective, we displayed a fixed image on several TN, IPS, and VA monitors including the ViewSonic VX922 (probably the strongest overdrive) and after 48H without a screensaver, changing anything or switching off, the display remained impeccable. Do we have to wait longer for the components “settle in”? If you have a doubt, activate the screensaver in case of prolonged non use. It will be best for your monitor, environment and electricity bill…

    To finish, we would like to thank the manufacturers who, except for HP and Conrac, agreed to be transparent and give us straight answers.

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