The influence of LED devices on the performance parameters of LED full-color display
Abstract: This article starts with the parameters of the LED device and analyzes the influence of various parameters of the LED device on the parameters of the full-screen LED full-color display, which has a guiding significance for the parameter control and quality improvement of the LED display.
I. Overview
LED full-color display is a new type of indoor and outdoor large-size electronic communication media. It has the characteristics of large size, good environmental adaptability, high brightness and dynamic playback. It is unique in the field of indoor and outdoor large-size electronic communication media. With the further improvement of cost performance, the application field is becoming wider and wider, and it is widely used in advertising, stage, signboard, transportation facilities, public places and other fields. In recent years, the Spring Festival Gala has used LED full-color display as the background and decoration. The stage design of the Spring Festival Gala in 2008, from the main scenes of frontal background, side background, and ceiling background, used a large number of LED full-color displays, which made the stage beautiful and the atmosphere was first-class. The application of the stage is only one aspect of the application of LED full-color displays. LED full-color displays are entering various application fields at an unprecedented speed.
Second, LED full-color display performance parameters
In recent years, China has become a global manufacturing center for LED full-color displays, and the level of technical quality has been continuously improved. With the improvement of technical level, users and manufacturers have increasingly higher requirements on various performance parameters of LED full-color display. About 70% of all performance parameters of LED full-color displays depend on the performance parameters of LED devices. Therefore, LED devices have become the most important key components of LED full-color displays. Strengthening the understanding of LED device performance parameters and choosing high-quality LED devices play an important and decisive role in improving the performance parameters of LED full-color displays.
3. The influence of LED device parameters on the performance parameters of LED full-color display
There are dozens of performance parameters for LED full-color display, including nearly 20 key parameters. The following describes the LED device parameters and the corresponding LED full-color display performance parameters one by one.
(1) Brightness
Brightness is the basic indicator of LED full-color display. The industry generally believes that outdoor display screens should be no less than 5000nits and indoor display screens should be no less than 1000nits. The brightness of the entire screen depends on the superposition of the brightness values ​​of the three LEDs of red, green, and blue that make up each pixel. The brightness values ​​of red, green, and blue are approximately in the ratio of 3: 6: 1. Set different current values ​​of red, green and blue on the basis of the factory nominal value of the device current to achieve the above ratio. For example: for outdoor P20 full-color display, 1800mcd for green tube, 900mcd for red tube, and 300mcd for blue tube, the brightness of each pixel is 3000mcd, and the maximum brightness of the whole screen is 2500 dots × 3000mcd = 7500nits. Finally, the brightness required by the specification can be achieved by adjusting the current value. The brightness is not as high as possible, it is suitable.
(2) Wavelength
LED full-color display is composed of three kinds of LEDs, red, green and blue, each color is measured by wavelength. The color of the display is closely related to this wavelength. The average wavelength of the red, green and blue LEDs of the display determines the dynamic color gamut of the LED full-color display. Generally speaking, the wavelength of the red LED is about 625nm, green is about 525nm, and blue is about 470nm. A high-quality LED full-color display should have a wide color gamut.
(3) Consistency
â‘ Brightness consistency
The brightness consistency of the LED full-color display depends on the brightness consistency of the LED device. Generally, the highest and lowest brightness ratio of each color of the LED device is not higher than 1.3, and then according to the scientific PCB insertion method, to ensure that the brightness difference between two adjacent LEDs of the same color is less than 10%.
â‘¡Color consistency
The LED devices that make up the LED full-color display all require a certain wavelength range. If the wavelength range is too wide, it will affect the consistency of the display chromaticity. Generally speaking, the wavelength range of each color of red, green and blue is required to be within 5nm.
â‘¢ Angle consistency
The full-color LED display is composed of LED devices with angles. The consistency of the angle of the LED device will seriously affect the consistency of the brightness and chromaticity of the display at different angles. The consistency of the red, green, and blue brightness of the LED device (especially the elliptical lamp) with the viewing angle also seriously affects the consistency of the brightness and chromaticity of the display screen at different angles. Among all the parameters of the full-color display, this parameter is the most difficult to reach. The difference between high-end LED full-color displays lies here.
(4) Power consumption
LED is a very energy-saving light-emitting device. The power consumption of the LED device determines the power consumption of the LED full-color display. Taking the P20 full-color outdoor display as an example, in the video playback state, the average power consumption is about 250W per square meter. For some advertisers that broadcast 24 hours, due to the large area and long playback time, power consumption is an indicator of their concern. LEDs with higher brightness can be used to make the display, so that low current can be used. Generally speaking, the nominal brightness of the red, green, and blue LEDs is increased by 20% each. When the brightness of the display is unchanged, the power consumption of the display will be reduced by 15%.
(5) Perspective
The viewing angle of the LED full-color display depends on the viewing angle of the LED device. At present, most outdoor display screens use elliptical LEDs with a horizontal viewing angle of 100 ° and a vertical viewing angle of 50 °, and indoor display screens use patch LEDs with a horizontal and vertical viewing angle of 120 °. Due to the particularity of the display screen on the highway, a circular LED with a 30 ° viewing angle is generally sufficient. The display screens on some tall buildings have high requirements on vertical viewing angles. The angle of view and brightness are contradictory to each other, and a large angle of view will inevitably reduce the brightness. The choice of perspective needs to be determined according to the specific use.
(6) Failure rate
An important indicator of the LED full-color display is the blind spot rate of the LED, which depends entirely on the quality of the LED device (excluding the effects of virtual soldering, soldering, and poor contact in the display production process). LED devices should undergo various types of sampling tests before leaving the factory, including a series of tests at room temperature lighting, high temperature and humidity, thermal shock, etc., to ensure product stability, consistency, and continuity. Generally speaking, the high-quality LED devices used for full-color displays have a failure rate of less than 1 in 10,000 in 1000 hours.
(7) Attenuation characteristics
The LED full-color display will show a decrease in brightness and inconsistent colors after a long period of operation, mainly due to the brightness attenuation of the LED device. The attenuation of LED brightness will cause the brightness of the entire screen of the display to decrease. The inconsistency of the brightness attenuation of red, green and blue LEDs will cause the inconsistency of the color of the LED display, which is what we often say the display takes. High-quality LED devices can well control the brightness attenuation. According to the standard of 1000mA lighting at normal temperature for 20 hours, the red attenuation should be less than 2%, and the blue and green attenuation should be less than 10%. % Of rated current.
In addition to the attenuation characteristics related to the characteristics of the red, green, and blue LEDs, the use of current, the heat dissipation design of the PCB, and the ambient temperature of the display screen all affect the attenuation.
(8) Size
The size of the LED device affects the pixel distance of the LED full-color display, that is, the resolution. The 5mm elliptical lamp is mainly used for outdoor display screens above P16, the 3mm elliptical lamp is mainly used for outdoor display screens of P12.5, P12, P10, and the 3528 SMD LED is mainly used for indoor display screens of P6 and P8. 5050 SMD LEDs are mainly used for semi-outdoor displays such as P16 and P12.5. Under the premise that the dot pitch is unchanged, the increase in the size of the LED device can increase the display area and reduce the graininess. However, because the black area decreases, the contrast will be reduced; on the contrary, the size of the LED decreases, reducing the display area, the graininess increases , The black area increases, increasing the contrast.
(9) Life
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 full-color display, so as long as the quality of the LED device is guaranteed, the operating current is appropriate, the PCB heat dissipation design is reasonable, and the display screen production process is rigorous, the LED device will be the display One of the most durable parts in the screen machine.
The LED device is the most important component of the LED full-color display, and its performance parameters play a decisive role in the performance parameters of the display, and its cost also accounts for half of the total cost of the display. Choosing, using, and understanding the influence of LED devices on the parameters of the display screen are very necessary for the design and manufacture of the display screen, especially for high-quality LED full-color display screens. At present, the domestic LED industry is developing rapidly. The technical level of LEDs used in full-color displays is comparable to foreign brands. The price is suitable. It has been widely used in major projects such as the 2008 Olympic Project and has performed well. Promote China's transformation from a large LED display manufacturing country to a strong LED display manufacturing country.
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