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I am developing a user interface on a cheap Kinco color LCD HMI unit. After leaving a test UI on the screen for about 3 days, there was a very decided "ghosting" effect.

I was able to eliminate the ghost outlines by alternating a solid black and white screen over the course of about 2 days. Now the screen is back to normal and the ghosted image does not appear.

Since this HMI will be in service for several years with basically the same screens always in use, I want to build a screen-saver which will prevent ghosting. Note that users will view/interact with the HMI very little, as it's in a remote location and may be visited a couple times per week.

In building a screen saver, should the display constantly alternate between solid black and white screens, or is there a specific color which places the least "strain" on an LCD pixel, which would avoid ghosting and ensure pixels remain as bright and color-accurate as possible? For example, is Black considered "full on" or "full off" by the LCD circuitry and pixels? Would a black or white pixel create more prominent ghost image, or is the issue going to appear for any pixel that does not change over a period of time?

I assume either black or white would be the default/resting state of a pixel (i.e. no driver current applied to the RGB subpixel elements) but I don't know which.

At this point I don't know whether alternating between colors is better or worse than filling the screen with a single, unchanging color. I'm looking to implement whichever scheme preserves the pixel brightness/dynamic response and eliminates ghosting.

Note that I did enable the auto backlight-off feature, but even when the backlight is off, the LCD is still displaying the image.

Your recommendations are appreciated.

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  • \$\begingroup\$ If the screens will be on 24/7, then you can alternate between black and white screen during the night. \$\endgroup\$ – Harry Svensson Dec 22 '17 at 20:03
  • \$\begingroup\$ The screen will be on 24/7 but will be used infrequently. It doesn't have to keep an image visible unless a user goes onsite and wakes it up. Otherwise, it will always (95% of the time) be in Screen Saver mode. My question relates to what is the best image/color to display to protect the pixels and prevent ghosting. \$\endgroup\$ – Ryan Griggs Dec 22 '17 at 20:06
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    \$\begingroup\$ Full white with the backlight dimmed seems to be highly recommended from the few googles I did. Including one from Apple. \$\endgroup\$ – Trevor_G Dec 22 '17 at 20:19
  • \$\begingroup\$ Why not turn the display completely off, as in use a mosfet to control the vcc? Seems like it would also extend the life of your product. \$\endgroup\$ – Ron Beyer Dec 23 '17 at 1:57
  • \$\begingroup\$ @ron it needs to be available anytime the users go onsite. They expect it to be ready to use without needing to power it on manually. Part of its role is to display the building entry alarm keypad so it needs to be on for that. Guess I could switch its 24vdc supply with a relay when the door opens... \$\endgroup\$ – Ryan Griggs Dec 23 '17 at 2:37
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I don't think any one color will be more "easy" on your display. The circuit and structure for a LCD monitor are the same for each color, they just have a color filter in front of them. There are other ways to do it with color changing backlights or color wheels, but that doesn't change the advice that the color doesn't matter.

enter image description here

--Edit @Trevor made me look up what the dominant behavior of LCD screens is and I didn't find a definitive answer. "It depends on the resting state of the LCD as to whether they require energy to stop light or to allow light to pass through," was one quote I read on Scientific American's website. What I was trying to say before was it depends on the construction of your LCD as to whether the no power state is black or white. You'd want to consult your datasheet or the manufacturer to find that piece of information and then put it in the off state for your particular device.

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    \$\begingroup\$ I've wondered whether black traps the heat inside the LCD - maybe more important for a projector than a monitor due to the light intensity. Would white allow more of the energy to escape as light rather than be absorbed by the dark pixels? \$\endgroup\$ – Transistor Dec 22 '17 at 20:33
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It is usually not a big issue in LCDs, they don't really burn in the classic sense, unlike say AMOLED (Spit!).

However the LEDs in the backlight have a finite life, and these far more then the LCD itself tend to determine the life of the display. For this reason my usual screen saver is to just dim the backlight way down.

You seem to have a screen which you say is ghosting? It may be worth having a look at the control chip register map, as you may be getting some DC across the liquid (never a good thing), also is it very cold where this thing is being deployed? LCDs can get very slow to respond in the cold.

One thing I found is that you often get reversed logic between off and on when switching from a TFT to an IPS panel even when using the same controller, make of that what you will.

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  • \$\begingroup\$ This is an all-in-one HMI unit with built-in LCD screen (anaheimautomation.com/products/hmi/…) so I can't modify the internal circuitry. Yes it exhibited very prominent ghosting after displaying a fixed image for only three days. \$\endgroup\$ – Ryan Griggs Dec 26 '17 at 21:47
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Something more dynamic like an alternating pixel checkerboard pattern may actually be more effective than a simple fixed pattern.

Moreover, if you can modulate the pattern to be a more sinusoidal transition between the two you may fine the net effect erases the residual faster.

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