TFT LCD Burn-in
Burn-in refers to the image residue phenomenon of oled or lcd screen. The causes of oled and lcd screen are different: oled is caused by the damage of organic light-emitting materials, while lcd screen is caused by the polarization of liquid crystal molecules in the electric field. OLED’s The burn-in phenomenon is irreversible. The slight burn-in problem of the LCD screen can be recovered, but it cannot be recovered when it is serious.
The word Burn-in is used to describe the adverse phenomenon of OLED display. OLED display uses current to make light emitting material emit light, and the life of light emitting material is limited, so when the technology is immature in the early stage, the life of light emitting material decreases, the burn-in phenomenon will appear. This phenomenon cannot be reversed, once it occurs, it means that your monitor has been damaged. Different pixel arrangements and pixel sizes and some display technologies are now used to extend the life of OLED displays.
LCD image sticking
What is Burn-in
The basic principle of TFT LCD is to use electric field to control the rotation Angle and direction of the liquid crystal to control whether the light passes through the color filter. The light can pass through the corresponding sub-pixel, and then the pixel will emit light. Tens of thousands of pixels compose the picture. And there is also a problem for TFT LCD display. When the LCD keeps a static picture for a long time, the liquid crystal molecules are polarized due to the long-term charge drive, resulting in the liquid crystal molecules can not be deflected normally under the control of signal voltage. This means that even if you change the contents of the display, you can still see traces of the still image on the screen. Image sticking is generally recoverable, and in extreme cases can cause permanent damage.
TFT LCD design has taken this into account, through VGH and VGL two voltage applied two positive and negative voltage to form a positive and two directions of the electric field, liquid crystal molecules in the display screen is constantly rotating. Even with such measures, some impurity ions are mixed into the liquid crystal during the manufacturing process of TFT. After a long time of fixed display, the ions move along the Angle of the liquid crystal to the upper and lower electrodes of the liquid crystal box until they reach the orientation layer. When the ions gather enough to affect the driving liquid crystal voltage, the penetration rate of the liquid crystal cell will be changed. At this time, if the display screen is switched, the aggregated ions cannot immediately leave the surface of the coordination layer. The rotation Angle of the liquid crystal molecules where the ions gather is different from that in other areas, and the light through is different, resulting in the formation of residual images.
Liquid crystal molecules in a positive electric field
Liquid crystal molecules in a negative electric field
Another important factor affecting image sticking is the flicker of the picture. Since TFT LCDS need to apply positive and negative voltage to the liquid crystal molecules, due to the different impedance of the line, there is actually a difference in the positive and negative voltage applied to the liquid crystal molecules, which results in the flicker of the picture. This problem is called flicker. Moreover, the imbalance of positive and negative electric fields will lead to more serious migration of magazine ions in the liquid crystal, aggravating the phenomenon of image sticking.
The relationship between flicker and burn in
Randomly check 47 displays from our production line to confirm the degree of flickering and burn in of the tft display, and count the defects:
Flicker=15% or less, the burn in phenomenon disappeared within 1min, the ratio is 20/47=42.55%.
Flicker=15%~17%, the phenomenon of burn in within 2 minutes is not visible or relatively slight, the ratio is 9/47=19.14%.
Flicker=17% or more, more than 3min burn in can still be seen, the ratio is 18/47=38.31%.
From the sample survey, we can see the relationship between Flicker and burn in (image sticking), so as long as Flicker is well controlled, the occurrence of burn in can be controlled and prevented.
We have a solution to this problem. Our products will use optical instruments to measure the flicker on each display and then use a program in the driver IC of the display to compensate for this deviation and ensure that flicker is eliminated. Although this increases our equipment investment and production efficiency, it can ensure that the products delivered to you must be perfect.
image sticking can also be better prevented in the use of products. The main way to produce image sticking is to display a static picture for a long time.
How to test the burn-in of the tft display
The black and white grid image remains in the burn in test
1. Use tft display to display a black and white grid picture or color bar picture, and display a 5×5 or 10×10 black and white grid picture according to the size of the display.
2. Keep the black and white grid picture or color bar picture for 10min, 20min, 30min.
3. According to the different requirements, switch the picture to the gray picture at different time periods (such as 10 minutes, 20 minutes, 30 minutes), and check whether there is a black and white grid picture left on the gray picture.
4. If there is no black and white grid image or color bar picture residue, then it proves that there is no burn-in phenomenon (also known as image sticking).
5. If the phenomenon of burn in occurs, it is necessary to observe the recovery time, if it is within 3 minutes, it is acceptable. If it cannot be restored after 3 minutes, it means that there is a problem with your display and needs to be debugged or repaired.
black and white grid test method
light up the black and white grid test pictures for different times as required
switch to grayscale screen inspection according to test requirements
black and white grid test failure phenomenon
color bar test method
Continuously display the color bar test picture for different times on request
Convert grayscale image to check
If the image sticking problem occurs, the color bar test screen will remain.
The longer the test screen is displayed, the higher the test temperature is, indicating the higher the test requirements. In addition, the black and white grid test picture is more difficult than the color bar test picture, and the black and white grid test picture is most commonly used.
So is there any way to avoid burn-in/image sticking? There are several ways to refer to it:
1. Avoid playing dynamic images or videos when you are not using your monitor by using a screen saver.
2. In the system design, some fixed ICONS such as power, signal and working state are designed as dynamic to reduce the existence of still pictures.
3. If your device has a startup logo, having this logo dynamic can help avoid image sticking.
4. Set the monitor to work at a suitable temperature, such as 20-30 degrees Celsius, because higher temperatures will speed up the movement of impurity ions, which will facilitate image sticking.
5. Avoid your equipment working in a state of high loading for a long time, because the equipment will generate more heat in a state of high load, and the temperature inside the equipment will be higher than you expected due to heat accumulation.
6. Do not let the display work in high brightness, LCD almost all use LED as a light source, and the way to increase LED brightness is to increase the current, which will not only make LED fever serious, but also make LED driver IC fever.
If your LCD is already Burn-in, you can try the following:
1. If it is a slight Burn-in problem, you can close your display and place it for 12-48 hours. The impurity ions in the LCD will slowly lose their effect, during which you can open the display and observe whether it has become better.
2. Properly heat the display. We already know that the Burn-in of TFT LCD is generated by ions in the liquid crystal. Heating the display after shutting down the display can increase the dissipation speed of charged ions. But the temperature should not be too high, polarizer and some of the film material in the back light source will be affected by deformation after heat display, in 40~45 degrees Celsius is more appropriate.
3. Play video to help eliminate image sticking while making sure your monitor doesn’t have a flicker problem, known as the flicker problem. Be aware, however, that if your monitor is sending flickering issues, playing video or images can aggravate image sticking!
Regarding the Burn-in of TFT LCDS, there is a general rule for image sticking in the TFT LCD industry, which is to switch to the white screen immediately after a display screen is displayed for 10-30 minutes, and then observe whether there is any graphic remains on the screen. If this standard can be met, then the display should be used without problems.