In order to protect the military parade marking the 70th anniversary of the victory of the Chinese People's War of Resistance Against Japanese Aggression and the World Anti-Fascist War, on September 1, two large LED screens were located on Tiananmen Square in Beijing. Two large LED outdoor full-color large screens have been built on the east and west side of Tiananmen Square. The large screens together with the base are about 18 meters high and 26 meters wide, and the entire screen is about 360 square meters. The official debugging lights up, and the effect is better than in previous years.
According to the person in charge, "Compared with previous years, this year's screen resolution is higher, and the image presentation will be clearer."
With the advancement of display technology, there has been a great improvement in brightness, clarity and quality. At present, it has been widely used in advertising, conferences, monitoring, stage rental, sports event broadcasting and other fields. The event site is still in small shopping malls and stores, which can be seen everywhere.
So, do you know the impact of LED lamp beads on LED display?
1. The key component of full-color LED display is LED lamp beads
1. LEDs are the most used key components in the full-color screen, and thousands to tens of thousands of LEDs are used per square meter;
2. LED is the main body that determines the performance of the entire optical display, which directly affects the audience's evaluation of the display;
3. LED accounts for the largest proportion of the overall cost of the display, ranging from 30 percent to 70 percent .
2. The chip and angle of view of the lamp bead
The viewing angle of the LED display depends on the viewing angle of the LED lamp beads. The quality of LED lamp beads depends on the technology of LED chips and packaging
At present, most outdoor displays use elliptical LEDs with a horizontal viewing angle of 100 degree and a vertical viewing angle of 50 degree , while indoor displays use SMD LEDs with both horizontal and vertical angles of 120 degree . The display screen on the highway generally chooses 30 degree due to its particularity; the circular LED with the viewing angle is enough.
Displays on some tall buildings require higher vertical viewing angles. The viewing angle and brightness are contradictory, and a large viewing angle will inevitably reduce the brightness. The choice of viewing angle needs to be determined according to the specific use.
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3. How to identify the advantages and disadvantages of LED display lamp beads?
1. Look at the solder joints
The LED light strips produced by regular LED light strip manufacturers are produced by SMT patch process, solder paste and reflow soldering process.
2. Look at the quality of FPC
FPC is divided into two types: copper-clad and rolled copper. The copper foil of the copper-clad plate is protruding. If you look closely, you can see it from the connection between the pad and the FPC.
3. Look at the cleanliness of the surface of the LED light strip
If the LED light strip produced by the SMT process is used, the cleanliness of the surface is very good, and no impurities and stains can be seen.
4. Look at the chips and production processes for LED lights
You can't tell the difference with your eyes. You need to use aging equipment and testing equipment. If you put several manufacturers' LEDs on the aging machine and use high current to age them for 24 hours or more, you will measure the LED brightness of several manufacturers. , look at the LED with the smallest attenuation of luminous intensity, and the quality with the smallest attenuation is the best.
Fourth, how to see the brightness of LED lamp beads?
1. LED brightness is the determining factor of display brightness. The higher the brightness of the LED, the greater the margin of the current used, which is good for saving power consumption and keeping the LED stable.
2. The LED has different angle values. When the brightness of the chip is fixed, the smaller the angle, the brighter the LED, but the smaller the viewing angle of the display. Generally, a 100-degree LED should be selected to ensure a sufficient viewing angle of the display.
For displays with different dot pitches and different viewing distances, a balance point should be found in brightness, angle and price.
3. Failure rate
Since the full-color display is composed of tens of thousands or even hundreds of thousands of pixels composed of three types of red, green, and blue LEDs, the failure of any color LED will affect the overall visual effect of the display.
Generally speaking, according to industry experience, the failure rate of LED display should not be higher than 3/10,000 (refers to the failure caused by the LED lamp bead itself) before the LED display starts to be assembled and aged for 72 hours before shipment.
4. Antistatic ability
LED is a semiconductor device, which is sensitive to static electricity and can easily lead to static electricity failure. Therefore, the anti-static ability is very important to the life of the display screen. Generally speaking, the failure voltage of LED human body electrostatic mode test should not be lower than 2000V.
5. Lifespan
The theoretical life of the LED device is 100,000 hours, which is much longer than the working life of other components of the LED display. Therefore, as long as the quality of the LED device is guaranteed, the working current is suitable, the PCB heat dissipation design is reasonable, and the display production process is rigorous, the LED device is the complete display device. One of the most durable parts in the world.
LED devices account for 70 percent of the price of LED displays, so LED devices can determine the quality of LED displays. my country is not only a big producer of LED devices, but also a gathering place for LED display production.
The high-tech requirements of LED display are the future development trend. The high-quality requirements of LED display are not only about the trend of LED display manufacturers, but also the development of LED display device manufacturers. From the control of LED devices, to promote China's transformation from a large LED display manufacturing country to a powerful LED display manufacturing country.
6. Attenuation characteristics
After the LED display works for a long time, there will be a phenomenon that the brightness decreases and the color of the display is inconsistent, which is mainly caused by the brightness attenuation of the LED device. The attenuation of LED brightness will reduce the brightness of the entire display screen. The inconsistency of the brightness attenuation of the red, green and blue LEDs will cause the inconsistency of the color of the LED display, which is the phenomenon that we often say that the display is spent.
High-quality LED devices can well control the magnitude of brightness attenuation. According to the standard of 20mA lighting for 1000 hours at room temperature, the red attenuation should be less than 2 percent , and the blue and green attenuation should be less than 10 percent . Therefore, try not to use 20mA current for blue and green LEDs in the design of the display screen, preferably only 70 percent to 80 percent . percent of rated current.
In addition to the attenuation characteristics related to the characteristics of the red, green and blue LEDs themselves, the current used, the heat dissipation design of the PCB board, and the ambient temperature of the display screen all affect the attenuation.
7. Consistency
No matter how good the white balance of the display is, if the angle consistency of the LEDs is not good, the white balance effect of different angles of the whole screen will be bad. The angle consistency characteristics of LED lamp beads can be measured by LED angle comprehensive tester, which is especially important for medium and high-end display screens.
The full-color display screen is composed of numerous pixels composed of red, green and blue LEDs. The consistency of the brightness and wavelength of each color LED determines the brightness consistency, white balance consistency and chromaticity consistency of the entire display screen. sex.
Generally speaking, display manufacturers require device suppliers to provide LEDs with a wavelength range of 5nm and a brightness range of 1:1.3. These indicators can be achieved by the device supplier through a spectroscopic color separation machine. The consistency of voltage is generally not required.
Since the LED is angled, the full-color LED display also has angular directionality, that is, its brightness will increase or decrease when viewed from different angles. In this way, the angle consistency of red, green, and blue LEDs will seriously affect the consistency of white balance at different angles, and directly affect the fidelity of the video color on the display.
To achieve the matching consistency of the brightness changes of the red, green and blue LEDs at different angles, it is necessary to strictly carry out scientific design in the design of the packaging lens and the selection of raw materials, which depends on the technical level of the packaging supplier.
