Hangzhou Xuhong Technology Co.,Ltd
EN
中文
When we use LCD display devices such as mobile phone, vehicle display, home appliance display, do we sometimes feel that there is a line rolling up and down on the screen? Sometimes the screen is flashing? Yes, this is the flash screen phenomenon. Below we will explain from three aspects: the reason, principle analysis and the solution.
ONE、 The reason analysis of flash screen phenomenon
There are several reasons for the flash screen of TFT LCD, roughly three types:
1. The similar frequency of the LCD screen and the ambient light source may cause flash screen phenomenon, most of the time the two frequencies are different, but there is a coincidence, it will cause the screen flashing.
2. The mismatch between the LCD module and the motherboard may cause the phenomenon of flash screen
3, The backlight resource may cause the flash screen phenomenon, which is the most common cause.
TWO、The principle analysis of flash screen caused by backlight resource
As we know, there are two types of backlight resource: one is LED backlight, LEDs (light-emitting diode) are used as the backlight of TFT LCD screens. The other is CCFL backlight, CCFL (cold cathode fluorescent tube) are used as the backlight of TFT LCD screens.
Compared with the traditional CCFL backlight, LED backlight has the characteristics of low power consumption, low heat generation, high brightness, and long lifetime. In terms of market share, now LED backlight is the mainstream, which is widely used in various LCD display fields such as home appliances, automotive, digital products, etc. However, TFT LCD screens with LED backlight are more prone to flash screen phenomenon. Especially for some sensitive eyes of customers, the splash screen is unfriendly, it may cause eye pain after long time using. So is it really the fault of the LED backlight? In fact, the key is PWM dimming.
So what is PWM dimming? We know that the brightness of the LED backlight is a certain value, in order to adjust the brightness of LCD screen, we need to keep the LED backlight constantly turning on and off, to adjust the brightness by adjusting time length of turning on and off. When users adjust the brightness, they are actually adjusting the time length of the backlight turning on and off, which is called PWM dimming, and in Chinese it is called pulse width modulation.
In the practical application of display products, the switching time of LED backlight on and off is very short. The display products using PWM dimming have operating frequency between 200Hz to1000Hz, and the human eye can hardly detect the change of light and dark when the frequency at 100Hz. The picture we see is always bright. In fact, the backlight of CCFL also uses PWM dimming, but the essence of CCFL is a cold cathode fluorescent lamp tube. There is a delay phenomenon of the process that the electrons in the fluorescent tube hit the phosphor to form a spot, there will be a visual stay, resulting in afterglow effect, therefore, the CCFL backlight flash screen situation is relatively much better. Although LCD backlight has the problem of flash screen, it is obvious at low brightness, so it will not change its mainstream status.
THREE、 The solution of LCD flash screen
When the flash screen is caused by the LCD backlight, one of the solutions is to use high frequency PWM dimming. The common LCD display products operate at a frequency of 200Hz~1000Hz. In some areas of LCD display, there are particular strict requirements on display effect, we can adjust the operating frequency up to 5000Hz or even higher, so that the human eye can’t feel the flash screen phenomenon, and put an end to the flash problem of LCD screen.
But the high frequency PWM dimming should be moderate, we will give the optimal scheme by considering from display products application demand, the cost, display effect and other aspects.
