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Backlight Bleeding

1. What is backlight bleeding?

It is a very common phenomenon that liquid crystal display panel and the frame are not tight 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.

2. The reason for backlight bleeding

There are two main reasons for backlight bleeding.

First, it is about technology.

We must know 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 the electrical field. LCD which is different from the direct view CRT is displaying digital images and vivid colors by using electrical-optical conversion and different excitation of R, G, B three colors.

And it has several advantages:

1. Beam has minimal geometrics distortion and nonlinear distortion.

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

3. It has a small volume, lightweight, and it is easy to be designed in flat.

4. It has a 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. Large-screen LCD has a low yield rate and a high cost because it adopts an integrated circuit manufacturing process,

2. There is a narrow viewing angle.

3. It will be smearing sometimes when displaying fast-moving images.

4. It has lower brightness.

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

Second, the extrusion is 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, compared with producing display panel. There is a slight leak between the 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 an all-black environment.

3. 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 an all-black environment. In this condition, backlight bleeding will not affect the using time, the response time, the brightness and other aspects of LCD.

4. The solution of backlight bleeding

We should not pay much attention since backlight bleeding does not affect the use of LCD, and manufacturers may not obey the return policy. 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 the high-quality display panel, carefully assembly 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, the return of the product will not be allowed by the vendor even there is slight backlight bleeding. But if you by a high-end LCD, you don’t have to worry about backlight bleeding, because you can enjoy excellent after-sale service for a high-quality product.

greg

greg

Hi, I'm Greg, sales manager of displaybly.com. I've been working in the display & touch industry for more than 10 years, and the purpose of this article is to share the knowledge from a Chinese supplier's perspective.
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