In order to quickly judge the quality of the LED Screens, from the perspective of all parties, the following 9 important items of the LED display are integrated. The first 8 items are suitable for general LED displays, and the 9th item is for small-pitch LED displays.
Maximum brightness
Refers to the brightness of each primary color of the LED display at the highest gray level and maximum brightness under a certain ambient illumination. In short, it is the brightness measured in the normal direction by using a light gun when the display screen is set to white 255 level using software.
The outdoor LED display has different requirements for the maximum brightness according to the environment in which it is used, because in situations where the ambient light is relatively strong, the brightness of the LED display is required to be higher, so that the public can clearly see what is displayed on the screen. Under normal circumstances, the south-north display has a lower maximum brightness requirement, as long as it reaches 4000CD / m2, and the north-south display requires the entire screen brightness to reach 7000CD / m2. South facing requirements are the same, because for some time, sunlight will directly shine on the LED screens. Theoretically, brightness requirements greater than 5500CD square meters are sufficient.
Color temperature
When we see on the display that the color of the image is inconsistent or different from the material, then our picture is seriously distorted, which is related to the color temperature of the white balance of the LED display. If the human eye directly looks at the display, its white balance The color temperature value is more suitable between 6500 and 8000K, and if it is a display used by a TV station, the actual color temperature of the screen needs to be adjusted to about 5500K, so that the picture on the display is real after recording and broadcasting through the camera. .
Refresh rate
The refresh rate refers to the number of times that the LED display information is completely displayed per second. The refresh frequency is too low, and the human eye will see the LED display jitter. Usually we will see the scanning lines appear when shooting with the camera. Generally, the human eye requires a refresh frequency of more than 300Hz, that is, as long as the refresh rate exceeds 300Hz, the LED screens will not feel jittery when viewed with the naked eye. If you use a camera to shoot, according to the different settings of different cameras, generally the minimum the scanning line cannot be captured above 600Hz.
High refresh can increase the brightness and color fidelity of the display. It can be detected with a digital camera. If it is a high refresh, the picture taken by the camera is very clear, without snowflakes and scanning lines. This indicator is particularly important when renting screens and TV broadcasts.
Wavelength
The wavelength determines whether the color is pure and consistent. The discrimination method is simple; how can you distinguish with your eyes if you don’t have professional equipment?
First: The whole screen is white, and the screen should be pure white without any other noise. If you think it is a bit reddish or bluish, it proves that there are problems with display materials and process quality control. Over time, it will get worse.
Second: Make red, green, and blue monochromatic colors. The color at the center wavelength is what we usually say is positive blue, positive red, and green. If the color is darker or lighter, it proves to be a partial wavelength. If a certain color is inconsistent, it is proved that the wave difference is too large. Within the range of the center wavelength of the high-quality display, the blue-green wave difference is controlled at 3nm, and the red wave difference is less than 5nm.
The perspective of the arc tube
The luminous viewing angle of the light-emitting tube refers to the angle formed between the two viewing directions on the same plane and the normal direction when the brightness in the viewing direction decreases to one-half of the brightness in the normal direction of the LED screen. Divided into horizontal viewing angle and vertical viewing angle.
For outdoor LED advertising displays, elliptical arc tubes or SMD LEDs are generally used. Oval LEDs have small angles and high brightness. The vertical viewing angle of SMD LEDs is much larger than that of elliptical tubes, but its brightness is smaller than that of elliptical tubes. From the user’s perspective, LEDs with different viewing angles should be selected based on the audience side of the LED display and the surrounding light environment.
For indoor LED screens, because of their low brightness requirements and a wide audience, SMD LEDs are the best choice. It should be noted that there are some manufacturers of LEDs in the market in order to reduce costs and confuse users. The brightness of LEDs is made higher and the viewing angle is smaller than that of conventional LEDs. This will cause LED display screens. When viewed from the front, the brightness is very high, but when the side is viewed at a relatively large angle, the image cannot be seen clearly.
In order to improve the brightness of small-sized LED chips, a small-angle package is usually used. Large-size packages do not require small-angle packages because they do not require such high brightness. Therefore, a large angle (110) with high brightness and low current is the best.
Circuit design section
The design and materials of the circuit board play a vital role in the stability and display effect of the LED screens. There are mainly the following requirements:
1. Material requirements: PCB board thickness, generally 1.6mm thickness; Material: FR-4 glass fiber board, some manufacturers may use FR-2 paper substrate in order to reduce costs; Copper foil thickness: Thickness of copper foil It cannot ignore the heat dissipation of PCB board and the stability of the circuit. The normal copper foil thickness is 35um (1Oz), and some manufacturers will use the 18um (0.5Oz) copper foil thickness as a secondary charge; then as a consumer How can the person discern it? An empty PCB can be distinguished by weight. Under normal circumstances, the heavier the better.
2. Several key points in design: connector, connector refers to the connection between the module and the module. There are two main types used in the market now, one is horn and the other is row.The advantage of the horn is that the cable can be held by two slots, and it is not prone to failure due to connector problems. For the choice of electrolytic capacitors and tantalum capacitors, for applications requiring long life, tantalum capacitors are undoubtedly the first choice. Where low cost is required, electrolytic capacitors are preferred.
Automated production equipment
Most of the LED display screens are electronic components, and static electricity is very harmful to electronic components. Sometimes static electricity directly breaks through the component and damages it. Sometimes it does not directly break through, but it leaves hidden dangers and side effects. The components are damaged after a period of use. In the electronics manufacturing industry, people have thought of many ways to deal with artificial static electricity, including wearing an electrostatic ring, wearing electrostatic clothes, using a clean room, and so on. In fact, the most effective method is to avoid touching electronic components by human hands as much as possible, and the use of automation equipment achieves this goal.
Average power
The square power consumption refers to the power consumption generated by an LED display of one square meter. The unit of power we usually say is watts / hour. For example, the power consumption of a one-square-meter LED display is 300 watts, so the display consumes 300 watts / hour of electricity per hour per square meter, which is 0.3 watts of electricity as we often say. LED display power consumption generally has two indicators, one is the maximum power consumption, and one is the use of power consumption. The maximum power consumption refers to the power consumption of the LED display at the maximum brightness. How to distinguish the maximum power consumption with the eyes?
The method is simple: look at the number of power supplies behind the box, multiply the maximum power of each power supply, and calculate the maximum power consumption of the square meter according to the size of the box. There are two types of power supplies, 200W and 300W.
Indoor small pitch: low light and high gray
Low brightness and high gray, specifically explained: When the brightness range of the small-pitch LED display is in the range of 100 cd / O-300 cd / O, the grayscale of the display screen is not lost, or the degree of grayscale loss is difficult to detect within range.
Low brightness and high gray will be one of the key factors to distinguish the high quality of small-pitch LED display products. For small-pitch products, the competition of LED screens will no longer be compared with others, but the brightness will be lower. Compared to someone’s display, you can reduce brightness without losing grayscale and picture quality. In other words, only the small-pitch led display with low brightness and high gray is a good product that meets user requirements and has competitive strength.
Under the indoor dark environment, the human eye looks at the small-pitch LED display screen with high brightness for a long time. The high brightness unique to LED often makes people feel dazzling, and even causes eye pain, tears and vision loss. Therefore, the brightness of the LED display screen is too high, which will bring visual fatigue to users of indoor applications, and may even cause irreparable eye damage! It can be said that the brightness of the small-pitch LED display is definitely not as high as possible, and its brightness must be reduced. A large number of tests show that the brightness range of the LED display is controlled in the brightness range of 100 cd / O-300 cd / O, and the human eye feels more comfortable.
But this problem cannot be solved by directly adjusting the brightness of the display. Because the conventional LED display has the characteristics of low brightness and low gray, which means that the brightness of the display will be accompanied by the loss of grayscale of the led screen.
