9 Important Items to Judge the Quality of LED Screens

    In order to quickly judge the quality of LED screens, the following 9 important items of LED screens are summarized from various viewpoints. The first 8 items are applicable to general LED display screens, and the 9th item is for small-pitch LED display screens.

1. Maximum brightness

Refers to the brightness of each primary color of the LED display screen at the highest grayscale and highest brightness under a certain ambient illumination. In short, it is the brightness measured by the light gun in 

the normal direction when the led screen is set to white 255 level using the software. For outdoor LED screens, there will be different requirements for maximum brightness according to the use environment. Under normal circumstances, the maximum brightness requirement for the display screen facing south and north is lower, as long as it reaches 4000CD/m2, while the led display  facing north and south requires the entire screen brightness to reach 7000CD/m2. The requirements for facing east, west and south are the same, because there will be a part of the time when sunlight will directly shine on the LED display screen. In theory, the brightness requirement is greater than 5500CD square meters.

2. Color temperature

When we see that the color of the image on the display screen is inconsistent or different from the material, our picture is seriously distorted. This is related to the color temperature of the white balance of the LED display. If the human eye directly views the led screen, the color temperature value of the white balance is more suitable between 6500 and 8000K. If it is a display screen used for TV broadcasts, the actual color temperature of the screen body needs to be adjusted to about 5500K, so that the picture on the display screen after being recorded and broadcast by the camera is real.

3. Refresh rate

The refresh rate refers to the number of times the information displayed on the LED display screen is fully displayed per second. If the refresh rate is too low, the human eye will see jitter when watching the LED display. Usually, we will see scan lines appear when shooting with a camera. Usually, the human eye requires a refresh rate of more than 300Hz, that is, as long as the refresh rate exceeds 300Hz, there will be no jitter when watching the LED display with the naked eye. If you use a camera to shoot, according to the different settings of different cameras, generally at least 600Hz is required to capture the scan lines. High refresh can improve the brightness and color fidelity of the display. It can be detected with a digital camera. If it is high refresh, the pictures taken by the camera are very clear, without snowflakes and scan lines. This indicator is especially important when renting screens and TV broadcasts.

4. Wavelength

The wavelength determines whether the color is pure and consistent. The method of distinguishing is very simple; if there is no professional equipment, how to distinguish it with your eyes? First: The whole screen is white, and the screen should be pure white without any other colors. If you think it is a little red or blue, it proves that there are problems with the display material and process quality control. It will become more and more serious after a long time of use. Second: Play red, green, and blue monochrome. The color of the center wavelength is what we usually call pure blue, red, and green. If it is a little darker or lighter, it proves that it is biased wavelength. If a certain color is inconsistent, it proves that the wave difference is too large. The blue-green wave difference of a high-quality display is controlled at 3nm within the range of the center wavelength, and the red wave difference is less than 5nm.

5. Viewing angle of the light-emitting tube

The luminous viewing angle of the light-emitting tube refers to the angle between the two viewing directions of the same plane and the normal direction when the brightness in the viewing direction drops to half of the brightness in the normal direction of the LED display. Divided into horizontal viewing angle and vertical viewing angle. For outdoor LED advertising display screens, elliptical light-emitting tubes or SMD light-emitting tubes are generally used. Elliptical light-emitting tubes have the characteristics of small angle and high brightness, while the vertical viewing angle of SMD light-emitting tubes is much larger than that of elliptical tubes, but its brightness is smaller than that of elliptical light-emitting tubes. From the user's perspective, light-emitting tubes with different viewing angles should be selected according to the audience of the LED display screen and the surrounding light environment. For indoor LED display screens, since their brightness requirements are low and their audience is generally wide, SMD light-emitting tubes are the best choice. It should be noted that some manufacturers of light-emitting tubes in the market now make the brightness of light-emitting tubes higher and the viewing angle smaller than that of conventional light-emitting tubes in order to reduce costs and confuse users. This will cause the brightness of the LED display screen to be very high when viewed from the front, but the image will not be clear when viewed from a larger angle from the side. In order to increase the brightness, small-sized LED chips usually use small-angle packaging. Large-sized ones do not need small-angle packaging because they do not need such high brightness. Therefore, large angle (110), high brightness and low current are the best.

6. Circuit design part

The design and materials of the circuit board play a vital role in the stability and display effect of the LED display screen. There are mainly the following requirements: 1. Material requirements: PCB thickness, generally 1.6mm thickness is used; Material: FR-4 fiberglass board, some manufacturers may use FR-2 paper substrate to reduce costs; Copper foil thickness: The thickness of copper foil has an important role in the heat dissipation of PCB board and the stability of circuit. The normal copper foil thickness is 35um (1Oz), while some manufacturers will use 18um (0.5Oz) copper foil thickness to pass off inferior products as good ones; So how can consumers distinguish? You can take an empty PCB and distinguish it by weight. Under normal circumstances, the heavier the better. 2. Several key points in design: Connectors, connectors refer to the connecting parts between modules. There are two main types used in the market now, one is horns and the other is pin headers. The advantage of horns is that they can hold the cable through two card positions, and it is not easy to have failures caused by connector problems; Regarding the choice of electrolytic capacitors and tantalum capacitors, tantalum capacitors are undoubtedly the first choice for occasions requiring long life, and electrolytic capacitors are the first choice for occasions requiring low prices.

7. Automated production equipment LED

The display screen contains mostly electronic components, and static electricity is very harmful to electronic components. Sometimes static electricity directly breaks down the components and damages them, and sometimes it does not break down directly, but leaves hidden dangers, and the side effect is that 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 static electricity rings, wearing static electricity clothes, using dust-free workshops, etc. In fact, the most effective way is to avoid human hands from touching electronic components as much as possible, and the use of automated equipment achieves this goal.

8. Average power consumption

Square power consumption refers to the power consumption generated by an LED display screen with an area of one square meter. The unit of electricity we usually say is watts/hour. For example, if the power consumption of a one-square-meter LED display screen is 300 watts, then this display screen will consume 300 watts/hour of electricity per square meter per hour, which is what we often call 0.3 kWh. The power consumption of LED display screens generally has two indicators, one is the maximum power consumption and the other is the power consumption. 

9. Indoor small spacing: low brightness and high gray

It is specifically explained as: when the brightness range of the small-pitch LED display is between 100cd/O and 300cd/O, the grayscale of the displayed image is not lost, or the degree of grayscale loss is within the range that is difficult for the human eye to perceive. Low brightness and high gray will be one of the key factors to distinguish the quality of small-pitch LED display products. For small-pitch products,the comparison is about whose led screen can reduce the brightness without losing grayscale and picture quality. When the human eye looks at a high-brightness, small-pitch LED screen at close range for a long time in a dark indoor environment, the high brightness of LED often makes people feel dazzling.  It can be said that the brightness of a small-pitch LED display screen is definitely not the higher the better, and its brightness must be reduced. A large number of tests have shown that the brightness range of the LED display screen is controlled in the brightness range of 100cd/O-300cd/O, and the human eye feels more comfortable. However, this problem cannot be solved by directly adjusting the brightness of the display screen. Because conventional LED screens have the characteristics of low brightness and low gray, that is, the reduction of the brightness of the display screen will be accompanied by the loss of grayscale of the picture.