What are the standards for judging the quality of LED displays? How to identify the quality grade of an LED display?
With the widespread use of LED displays in various fields, more and more people are becoming familiar with and using them. So, how do we judge the quality of a display and choose a high-performance product that suits our needs? This requires us to understand the basic technical specifications of LED displays and primarily assess their quality grade from two aspects: functionality and performance.
First, let's look at the functionality of the display. The basic function of a display device is to play and display various text, images, videos, and other materials to a wider audience. The most important aspect is the realistic representation of the material, which requires the display to have extremely high fidelity. Improving fidelity is mainly achieved through the following technical indicators.
1. Brightness
Brightness provides a very intuitive sense of level, easily discernible at a glance. Don't assume that higher brightness is always better. It depends on your environment and viewing distance. Indoor displays are generally around 50°C, outdoor displays are above 50°C, and semi-outdoor displays are between 50°C and 60°C. Small-pitch displays require even lower brightness, around 50°C to 60°C. The key is to ensure the image is clearly visible in different environments without causing eye strain during prolonged viewing.
2. Color Temperature
When the colors of an image on a display don't match the source material, the picture is severely distorted. This is related to the display's white balance color temperature. For direct human viewing, a white balance color temperature between 50°C and 60°C is suitable. However, for displays used in television broadcasts, the actual color temperature needs to be adjusted to around 50°C to ensure a realistic image after recording and broadcasting.
3. Viewing Angle
For display devices, a wider viewing angle is always better, as it allows for a larger viewing area. The viewing angle of a display screen is divided into horizontal and vertical viewing angles. Currently, indoor full-color screens can achieve a horizontal viewing angle of over 90 degrees and a vertical viewing angle of over 90 degrees, while outdoor full-color screens have a horizontal viewing angle of over 90 degrees and a vertical viewing angle of over 90 degrees. Within the viewing angle range, while ensuring a clear and complete image, there should be no color distortion at different viewing angles. This is mainly related to the arrangement of the RGB chips in the LED lights. Currently, there are two arrangement methods on the market: triangular and vertical. The effect comparison is shown in the following figure:
4. Grayscale
When the image on the display screen has poor layering and pixel loss appears when compared with the source material, it indicates that the grayscale level of the screen is low and cannot fully and clearly present the content. The professional testing method is the grayscale bar test, which can intuitively show the grayscale level. The current grayscale level achievable in the industry is [not specified], and will be further improved in the future. The following figure shows a grayscale bar test diagram:
5. Refresh Rate
When the human eye directly views the display screen and the image appears flickering, or when a camera or camcorder captures many horizontal dark lines, it indicates that the refresh rate of the screen is low. To ensure optimal viewing without affecting the human eye, the refresh rate of a display screen should not be lower than a certain threshold. To meet the requirements of cameras and camcorders, the refresh rate needs to reach a certain level. The image below compares the effects of high and low refresh rates:
6. Contrast Ratio
When viewing the screen, if the image appears slightly washed out or hazy, as if a thin veil is on the surface, and the image lacks clarity, this indicates low contrast. This is mainly related to the LED packaging and module mask design. LEDs with black brackets have significantly higher contrast than those with white brackets.
7. Uniformity
Whether the display screen image is clean and free of speckles or mosaic effects is primarily related to the brightness and color consistency of the LEDs. We can test the screen's brightness and color uniformity in RGB monochrome and white states. The image below compares the test results and image effects:
After understanding the functions of a display screen, a display screen with excellent display effects also needs good performance to be considered a high-quality display screen. We mainly assess its performance through the following aspects:
(1) Pixel Defect Points (within the warranty period): Pixel defect points are divided into dead pixels and constant bright pixels. The following figure shows the industry standard level: With the advent of small-pitch screens, the industry standard is no longer applicable to small-pitch screens. The standard should be higher, and the defect rate should be controlled within -5%.
(2) Protection Level and Safety: Protection level mainly refers to waterproofing and dustproofing. The higher the IP value, the higher the protection level. The following figure shows the industry standard: Safety is mainly reflected in two aspects: first, leakage current, which is ≤3.5mA to ground under the condition of u-rated x 1.1 times; second, dielectric strength, with no insulation breakdown under the 1, 1 min test conditions. (3) Energy Consumption and Efficiency: To reduce the power consumption of the display screen, improve energy efficiency, thereby reducing the screen temperature and extending its service life, a 10°C temperature reduction doubles the product's lifespan. This is mainly achieved through the following aspects: a) Low VF value LEDs; b) Low VDS value constant current drive ICC; c) Low impedance PCB design; d) Module operating voltage; e) Switching power supply PFC ≥ 0.95% conversion efficiency (≥ 0.85%).
(4) Reliability: Even if a display screen has excellent display effects, if its reliability is low and its failure rate is unstable, then this... The display screen's quality is also quite low. To improve its reliability, the following aspects should be considered:
a) Material selection: Material analysis
b) Thermal design: Heat dissipation, heat distribution
c) Redundancy: Switching power supply, controller, PCB circuitry
d) Material tolerance: 20% margin
e) Reliability simulation verification testing: Lifespan, certification
After studying the product's functions and performance in detail above, when we look at a display screen again, we will know how to identify its quality level, thus achieving the goal of choosing a high-performance, cost-effective product that suits our needs.