How to buy the best led display screens from China? Published：2018-09-03
Full-color LED display consists of a combination of a light emitting diode array, so the quality of the LED directly affect the overall quality of the display. There are five factiors that determines the quality of LED: brightness and viewing angle, uniformity and clarity, the pixels out of control rate, life expectancy, energy consumption and energy efficiency. Factors affecting the life of the LED display are devided into internal factors and external factors. Internal factors include the performance of accessories, the performance of LED devices, products, anti-fatigue properties; external factors include working environment with LED display and so on. Cooling is a key factor that affects the quality and life of the LED display.
LED display of the five key indicators
LED (light emitting diode) display like the importance of automobile engines, air conditioning compressors. Choose a good performance LED is the completion of the basic conditions for a high-performance LED video display. However, even with the same side dishes, the same spices, the same stove, cook different levels may vary cook dishes. Therefore, the ability to make good use of LED display manufacturer is testing the touchstone. It is generally believed that the display the following five key performance indicators and LED quality parameters are closely related: the brightness and viewing angle, uniformity and clarity, the pixels out of control rate, life expectancy, energy consumption and energy efficiency.
1, brightness and viewing angle
LED display brightness depends on the density of luminous intensity and LED. In recent years, new technology in LED substrate, epitaxy, chip packaging and other aspects of the emerging, especially indium tin oxide (ITO) current spreading layer technology and process stability and maturity, the LED luminous intensity has been greatly improved. Currently, the world-class brand of small power LED in the horizontal viewing angle of 110 degrees vertical viewing angle is 50 degrees, the luminous intensity of the green tube has up to 4000mcd, red tubes up to 1500mcd, blue tube of 1000mcd. In the pixel pitch at 20mm, The display brightness can be achieved 10000nit above. Display can work around the clock in any environment.
When it comes to the display viewing angle, there is a phenomenon worthy of our consideration: LED display panel, especially outdoor display, people viewing angle substantially from the bottom and the product shape to the existing LED display point of view, there is half flux vanishing into the sky. In today's energy crisis, we have a more reasonable way to solve? Worth pondering.
2, uniformity and clarity
LED display technology development today, the uniformity has become the most important measure of the merits of the display. It is often said LED display "little bit brilliant, brilliant piece" is an image of a serious unevenness between pixels and modules metaphor. Professional thing to say is "dirt effect" and "mosaic."
Root causes uneven phenomenon are: the inconsistent LED performance parameters; display production, installation assembly insufficient accuracy; electrical parameters is not enough consistency to other electronic components; module, PCB design is not standardized.
Where the "inconsistencies of the LED performance parameters" is the main reason. These inconsistent performance parameters include: light intensity is inconsistent, the optical axis is inconsistent, inconsistent color coordinates, inconsistent color light intensity distribution curve of each group, and attenuation characteristics inconsistent. How to solve the inconsistency LED performance parameters, there are two main industry technical ways: First, by further subdivision of the LED specifications, and improve the performance of the LED consistency; the second is through a subsequent correction way to improve the display uniformity. Subsequent correction modules from the early correction, the correction module, to today's by-point correction. Correction from the simple correction of the light intensity, the development of light intensity, color coordinates correction.
However, we believe that the subsequent correction is not a panacea. Wherein the optical axis is inconsistent, the light intensity distribution curve is inconsistent, inconsistent attenuation characteristics, poor accuracy and assembly design is not standardized, it can not be corrected by follow-up to eliminate even this correction will follow the optical axis, attenuation, assembling accuracy of inconsistent worse.
Therefore, we conclude that the practice: Subsequent correction is only symptomatic, while the LED segment is the fundamental parameters, LED display is the future mainstream industry.
In terms of the relationship between the display uniformity and clarity, the industry there is often a misunderstanding on the understanding that a resolution to replace resolution. In fact, the display resolution of the display resolution of the human eye, uniformity (SNR), brightness, contrast and many other factors of subjective feelings. Purely physical pixel pitch reduced to improve the resolution, to the neglect of uniformity, to improve the clarity is no doubt. Imagine a grave there, "dirt effect" and "mosaic" of the screen, even though its physical pixel pitch and then a small, high resolution, and then, it is impossible to get a good image clarity.
Thus, in a sense, the current constraints to improve the clarity of the LED display is the main cause of "uniformity" instead of "physical pixel pitch."
3, the display pixel runaway
Many causes the display pixels out of control, the most important reason is that "LED failure."
LED main cause of failure can be divided into two aspects: First, LED itself is poor quality; the second is to use improper methods. Through analysis we summarize the correspondence between the LED and the two main cause of the failure mode between.
We talked about a lot of the above LED failure LED usually routine inspection tests can not be found. In addition to electrostatic discharge, large current (excessive junction temperature caused), improper use of the external force, etc., many LED failure at high temperatures, low temperatures, rapid changes in temperature or other adverse conditions, the LED chip, an epoxy resin, bracket the difference in the lead, solid crystal plastic, PPA cup materials such as thermal expansion coefficient, which lead to different internal stress generated, therefore, the quality of detection LED is a very complex task.
Furthermore, the GaN-based LED, the electrostatic discharge is the biggest cause of their failure. LED failure due to electrostatic discharge mechanism is very complex, equipment, tools, utensils and human are possible with static electricity and discharge it, such an electrostatic ranging from several hundred volts, the high tens of thousands of volts, the discharge time at the nanosecond level . We display production, installation, use blue-green occurred during pipe failure is often the LED-PN junction breakdown by electrostatic discharge actions. International Association of strict requirements of the standard static electrostatic discharge mode is divided into the Human Body Model (HBM) and machine discharge mode (MM). Of the device electrostatic discharge sensitivity (ESDS) is divided into three levels (Human Body Model): Level 1 is 0 ~ 1999V; Level 2 is 2000 ~ 3999V; level 3 is above 4000V. Generally LED electrostatic discharge sensitivity mode in the human body between a few hundred volts - thousands of volts, while in the machine mode only about five hundred volts to tens of volts. LED display due to the production process complicated, hard to detect electrostatic discharge, therefore, LED ESD sensitivity level 2 or above should be selected for the proper (Human Body Model), and electrostatic protection must run through the entire production process.