Backlight Bleeding

 What is backlight bleeding

It is a very common phenomenon that liquid crystal display panel and the frame are not close enough that some lights are transmittance out. It is inevitable to some extent and only a matter of how serious it is. Low-end display panels are more serious, meanwhile high-end display panels are better.

The reason for backlight bleeding

There are two main reasons for backlight bleeding.

First, it is technology.

We must know that the principles of LCD. Electrical-optical conversion is that the outer light transmittance is changed because the alignment direction of liquid crystal molecules is changed by electric field. LCD which is different from direct view CRT is displaying digital images and vivid color by using electrical-optical conversion and R, G, B three colors different excitation.

And it has several advantages:

1. Beam has minimal geometrics distortion and nonlinear distortion.

2. Beam position and gradient are not affected by the magnetic field.

3. It has a small volume, light weight, and it is easy to be design in flat.

4. It is digital orientation and high frequency display which can eliminate the interline flicker and large area image flicker.

5. It is better at anti-explosion and anti-radiation.

6. It is low power consumption which has a certain advantage in the medium and small screen display (such as laptops).

There are some disadvantages of LCD.

1. Because it is adopts integrated circuit manufacturing process, large screen LCD has a low yield rate and a high cost.

2. There is a small viewing angle.

3. When playing fast moving images, it will be smearing sometime.

4. It has lower brightness.

Liquid crystal is sandwiched between two layers of glass which are upper layer CF glass and lower layer TFT glass. The surface of two layers of glass is uneven. In order to grip and arrange the liquid crystal, the interface to two glasses is coated with a layer of PI (polyimide), and then it is rubbed by a cloth. So, this kind of backlight bleeding is inevitable. But more often than ever, they are invisible. Some panels cause serious backlight bleeding because of poor quality or transportation problems that will be detected by productive process and are insulated. So it is obvious that some backlight bleeding liquid crystal display panels are not caused by this reason.

Second, the extrusion caused by assembling LCD.This is the most important reason of backlight breeding. It is relatively loosing requirement, dirty environment and rough process for assembling LCD, comparing with producing display panel. There is a slight leak between display panel and the frame when LCD is assembled. But it is very difficult to be seen by naked eyes, and we can clearly see the backlight bleeding only in all black environment.

The relevant provisions of backlight bleeding

There is a law in our country  that luminous flux of backlight bleeding must be less than 4 cd / ㎡ in all black environment.  In this condition, backlight bleeding will not affect LCD the using time, the response time, the brightness and other aspects of LCD.

The solution of backlight bleeding

We should not pay much attention since backlight bleeding does not affect the using of LCD, and manufacturers will not replace it. It is completely normal that there is a slight backlight bleeding in the assembling LCD. High-end LCD barely has any serious backlight bleeding situation because of high quality display panel, carefully assembling process and excellent display design. For example: EIZO and NEC.

If you buy a low-end LCD, you have to check the LCD very carefully, otherwise a vendor will not replace it even there is a slight backlight bleeding. But if you by a high-end LCD, you don’t have to worry about backlight bleeding, and high quality and excellent service should be obtained.

 

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