Discussion on quality improvement of LED display screen

Along with the transformation of government functions, the Department of public information, service to the people and commitment to advancing, the establishment of a large area of information media, excellent performance, reliable quality for engineering and technical personnel concerned. According to the different applications of display performance and different requirements of display system cost, monochrome, dual color or full color LED display with its large size, high brightness, environmental adaptability of irreplaceable advantages, is widely used in the Performing Arts Center, waiting rooms, exhibition halls and other indoor and outdoor video display, whether it is day or night that sunny or cloudy, can let the audience see clearly shown, and can automatically adjust the video playing according to changes in the external natural light intensity. The biggest feature of the LED display is that it is not limited by the area, can reach tens or even hundreds of square meters or more, for displaying text, graphics, images, animation, video images and other information. The use of LED devices to produce large flat panel display system has become an important area of LED device applications, and thus promote the continuous improvement of LED manufacturing technology.

As national semiconductor light emitting device application of product quality supervision and inspection center, we undertake many LED display bidding quality testing, customer quality inspection. We SJ/T11141-2003 "according to the standard of Ministry of Information Industry General specification" LED "display and SJ/T11281-2007 light emitting diode (LED) display test method", to display product quality testing, the testing items of brightness and angle of view, uniformity and clarity, pixel rate, environmental protection and safety control requirements. Judging from the results of the test, the quality of the display screen produced by different enterprises is uneven, the analysis of the reasons, mainly in the following areas, should cause enough attention to production enterprises.

1, brightness and visual angle

Brightness is an important index of the display, the screen brightness density mainly depends on the luminescent intensity of LED and LED on the display screen. Some are installed on the higher walls of the display, LED pipe installation angle for the human eye to determine the intensity of light also has a certain impact. According to the SJ/T11141-2003 standard of Ministry of information industry, brightness is defined as the luminous intensity per unit area of LED display. When the brightness of the viewing direction is decreased to 1/2 of the luminance of the normal direction of the LED display screen, the angle between the direction of the observation and the normal direction of the same plane is divided into horizontal and vertical angles of view. Display color is a single color, double color and full color, the use of two types of environment: indoor and outdoor display screen, both the parameters of the selection and requirements are also different. Indoor full color brightness to above 800cd/m2, the brightness of outdoor full color in 1500cd/m2 above, to ensure the normal work of the brightness of the image display. New technology emerge in an endless stream of LED in recent years, substrate epitaxy, chip and package etc., especially indium tin oxide (ITO) material, current spreading layer technology and process stable and mature, so that the luminous efficiency of LED has been greatly improved. At present, most outdoor full color display can be greater than 120 degrees horizontal angle and vertical angle greater than 45 degrees, the pixel spacing is 16mm, full-color display brightness of white balance is greater than 6000cd/m2, pixel spacing is 20mm, full-color display brightness of white balance can be reached more than 5500cd/m2, the display screen can work all-weather in any environment.

LED tube light intensity depends on the tube current, the current 1W LED tube, the working current of the manufacturer's recommended for general 350mA. increases the working current, will improve the luminous intensity of LED tube, but also will cause fever of LED tube, LED tube to accelerate the decay, will actually affect the whole life LED display, LED tube is unlikely to be a replacement, therefore, once the screen has a larger number of LED end of life, it means that the termination of the display life. In a certain sense, the life of the LED tube determines the life of the display. The lifetime of the LED tube is usually the lifetime of the decay of the luminous intensity to 50% of the initial value. We found in the examination, the government procurement project now requires the supplier to provide quality inspection reports display, because it is the quality assurance before the bidding, the supplier sent inspection samples are selected, and the quality of these samples is reduced, product inspection is passed. Now the government procurement of products have quality requirements and price requirements, which generally accounted for 45 percentage points of the price, if the quality difference is not large, the price plays a key role. Now the supplier bids regardless of whether the product quality can meet the requirements, fill in the satisfaction, superior, on-site review is difficult to check, only after the successful bid, the procurement unit can be found. It is entirely possible to replace a good pipe with a poor quality pipe for a supplier who has won the bid at a low price. So in the choice of display products, as far as possible to choose a good reputation, brand ring of professional manufacturers, suppliers may also be required to provide LED tube purchase invoices to ensure the quality of LED tube and display.

2, uniformity and clarity

LED display three indicators reflect the uniformity of pixel intensity uniformity and brightness uniformity of display module and module brightness uniformity. Because the test pixel intensity uniformity to the LED tube removed from the display, process complex, but may also damage the pipe, so the screen test module or modules generally choose brightness uniformity as assessment indicators. Module luminance uniformity is the same block