LCD grade classification

When users purchase LCD monitors, they often listen to businesses saying: "The xx brand is good, use the A screen, xx card is not, use the B screen." What is the difference between A-screen and B-screen?

Grade A screens have higher grades than Grade B screens, and grade C grades have the lowest grades. In addition to these three levels, there is also a title that is "super A grade" or "AA grade", that is, a slightly higher product than A grade. Generally speaking, Grade B and Grade C are considered inferior products. Compared with Grade A, Grade B and Grade C have more bad spots, relatively uneven brightness, and the appearance may be damaged, and the price gap with Class A screen It may be as high as nearly one thousand yuan.

For Samsung, Philips, LG, these well-known brands, for the quality of the LCD screen is also relatively high, many will use "A" level screen to ensure quality. Therefore, in the procurement process, the price is not completely in accordance with a simple brand, but it strictly follows a cost manufacturing principle.

Bad points are irreparable pixels on the LCD panel that are produced during the production process. Behind the liquid crystal pixel there are three transistors, corresponding to the three filters of red, green, and blue. Any problem with any transistor will make this pixel a dead pixel. For a 15 inch 1024*768 screen, a total of about 1024*768*3=2,359,296 pixels are required, and a separate drive tube is integrated behind each liquid crystal pixel, in so many pixels and drive tubes. It is inevitable that there will be individual problems. The number of dead spots is directly related to the manufacturer's technology and process level. For now, each batch of LCD panels produced has usually 20% of its products have a bad point. With the continuous improvement of technology, the bad point rate of some brands of LCD panels has been able to control to less than 10%, but the 0 bad dot rate is still rare.

The bright spot is the red and green blue and blue dots that are displayed on the screen when the screen on the setup screen is completely black.

Dark spots are points on the screen that do not show color when the screen is set to be completely white or the same color.

In fact, the LCD panel discriminates not only the number of bad spots and bright spots, but also the difference between the color purity and the viewing angle. The manufacturer must use the comprehensive evaluation of these product pointers before they can grade the LCD as A grade. Class B and Class C, and will be based on the pricing of the product, which A-level screen and B-level screen must use a dedicated instrument to test, difficult to distinguish naked eye.

The panel manufacturers around the country have different levels of products:

Korean manufacturers, three of which are A-level Japanese manufacturers, five of which are A-class Taiwan-based manufacturers, and eight of which are A-class mainstream LCD monitors have the following nominal standards:

AA grade: LCD monitor without any dead pixels is AA grade.

Level A: Below 3 bad spots, no more than one bright spot, and the bright spot is not in the center area of ​​the screen.

Level B: Below 3 bad spots, with no more than 2 bright spots, and the bright spots are not in the central area of ​​the screen.

4 Identification In 2006, the liquid crystal display won the limelight on the market. Along with the long period of substantial price decline, LCD monitors have become the darling of consumers. When consumers choose among various brands of liquid crystal displays, the most powerful basis is often the performance parameters of liquid crystal displays. The terms “response time, contrast, brightness, and viewing angle” are familiar performance parameters for consumers, and the only concept that is not known is the level of LCD panels. The author will describe the concept of the level of LCD panels in this contribution. Consumers may use LCD monitors, especially low-priced products.

The bad point Before introducing the level of the LCD panel, I first introduced to you readers the specific concept of the "dead point" existing on the LCD panel, so that later on this basis to distinguish the level of the LCD panel. The LCD panel is composed of a large number of pixels. Both of them can display black and white and red, yellow and blue primary colors. By combining the pixels with different colors, we can see the image displayed on the LCD panel. However, a few pixels on the LCD panel cannot produce color changes. Regardless of the image displayed on the LCD screen, these pixels always display the same color. These faulty pixels cannot be repaired and can only be replaced by replacing the entire LCD panel. These faulty pixels are usually divided into two categories. The “dark point” is a “dark point” that cannot be displayed regardless of how the screen display image changes. What’s even more annoying is that it always glows as long as it is turned on. The "highlights".

With the development of LCD technology in 2013, it still cannot fundamentally overcome this defect. Because the liquid crystal panel consists of two glass plates, the middle sandwich is a crystal droplet of about 5 microns in thickness. These crystal droplets are evenly spaced and contained in tiny cells, each of which constitutes a pixel on the screen. Under the magnifying glass, pixels are square, and a pixel is a luminous point. Each light-emitting point has its own transistor to control the strength of its current. If the transistor controlling this point is broken, the light spot will always be lit or not lit. This is the bright spot or dark spot mentioned above, collectively referred to as "bad point"!

The grade LCD panel can be divided into three grades: A, B, and C according to quality. The grade discrimination is based on the number of dead pixels. However, there are no relevant rigid rules in the world, so the standards for different countries and regions are not the same. Under normal circumstances, the number of dead pixels in a liquid crystal panel is less than 5, which is class A. The number of dead pixels is more than 5, and less than 10 are class B. If the number of dead pixels is more than 10, they are class C panels. In principle, A-class panels are most suitable for the production of displays, but the production of B-level panels for LCD panels is also an unavoidable issue. Therefore, most of these B-level panels will also be digested by the makers of no-name displays. The C-class panel is completely unsuitable for the manufacture of displays, and is mostly cut into small-area liquid crystal panels for use in other fields. However, there are also a few LCD makers that use C-class panels. Two or three years ago, there were low-quality LCD monitors that disrupted the market.

Of course, in addition to the number of dead pixels, the performance of Class B and Class C panels in other aspects cannot be compared with Class A panels. Compared with Class A panels, the brightness of Class B and Class C panels is relatively uneven, the color saturation is relatively insufficient, the image color reproduction ability is poor, and the appearance may even be damaged. In addition to using professional instruments to determine the level of LCD panels, consumers can also use the naked eye for intuitive identification. It is best to use the known A-class panels for comparison. Class B and C panels will appear immediately. In addition, panel makers also classify A-level panels into three steps: A++, A+, and A. The best-quality LCD panels are suitable for consumers with higher display quality requirements. In general, there are fewer than three dark spots on the A-class panel and fewer than three bright spots, while the sum of bright spots and bad spots is less than five; the number of dark spots on the A+ class panel is less than three, and The entire screen has no bright spots, and the number of dead pixels is less than 3; the A++ class panel has neither bright spots nor dark spots, and the number of dead pixels is zero. A small number of LCD manufacturers claim that their display products have no bright spots, and their LCD monitors use A+ class panels.

Panel identification methods As competition has intensified and technological processes have improved, manufacturers of LCD screens have increased their raw material standards. Internal quality control such as production and inspection has been strengthened, and the frequency of bad spots has been greatly reduced. The method of detecting dead pixels is also relatively simple. As long as the brightness and contrast of the LCD screen are turned to the maximum (displaying a reversed white screen) or to the minimum (displaying a full black screen), the number of bright spots on the screen and how much Dark spots. As long as the number of dead pixels does not exceed a certain standard, it is normal to have more than one dead pixel, but it is best not to fall below the level A panel standard.

In addition, you can use professional testing software to test other indicators of the LCD monitor. For example, the NOKIAMONITORTEST software is a test program that consumers can take with them on the disk. This software provides a total of 15 options, namely Geometry, Brightness and contrast, High Voltage, Colors, Tocontrolpanel/display, Convergence, Focus, Resolution, Moire, Readability, Jitter, and Sound. For the liquid crystal display, in addition to not being able to test the response time, the other main performance parameters are exhaustive, and the consumer's concern is even more difficult. If the monitor's color purity, contrast, and darkness are problematic, Class B and Class C panels will have nothing to hide.

Brand B- and C-class panels should have been used as defective panels that have been eliminated or used for other purposes, but have been adopted by a few display manufacturers because of their low price and profitability. The incident that caused class B panels to infiltrate the market is the result. Therefore, when consumers purchase liquid crystal displays, they must pay attention to the quality of liquid crystal displays. Unless the manufacturer explicitly declares that he has adopted an A-level or higher LCD panel, he still buys a brand with a better reputation. The display is definitely one of the most competitive areas of the current competition. This phenomenon has continued from the CRT display era to the LCD era.

Samsung, LG, Philips, BenQ, and ViewSonic are among the top five manufacturers in the display industry. The top five manufacturers started the LCD market earlier. With the advantages of preconceived, coupled with the brand awareness created in the entire display area, the five major display manufacturers have gained recognition from numerous users in the liquid crystal display market, and have also gained a large market share. As we all know, the difficulty of building a brand is considerable. Therefore, for five first-line manufacturers, the use of B-class panels is definitely worth the candle, so their products are still trustworthy. The other is AOC these "new" manufacturers, their products also dare to play "no bright spots" slogan, also worthy of consumer trust.