How to choose LED display package device to see brightness and viewing angle

· Display brightness depends mainly on LED luminous intensity and LED density

· Display angle should solve the problem of luminous flux waste

The brightness of the display depends mainly on the luminous intensity of the LED and the density of the LED. In recent years, new technologies for LEDs in substrates, epitaxy, chips and packages have emerged, especially the stability and maturity of indium tin oxide (ITO) current spreading layer technology and technology, which has greatly improved the luminous intensity of LEDs. At present, the world-class brand low-power LED has a horizontal viewing angle of 110 degrees and a vertical viewing angle of 50 degrees. The luminous intensity of the green tube has reached 4000mcd, the red tube has reached 1500mcd, and the blue tube has reached 1000mcd. When the pixel pitch is 20mm, the display brightness can reach 10000nit or more. The display works 24/7 in any environment.

When it comes to the viewing angle of the display, there is a phenomenon worthy of our consideration: LED display, especially the outdoor display, people's observation angle is basically from the bottom up, and from the product form of the existing LED display, there are Half of the luminous flux disappeared into the sky. In today's energy shortage, do we have a more reasonable solution? Worth pondering.

How to choose LED display package device to see uniformity and clarity

·Inconsistent LED performance parameters are the main factors affecting uniformity

· The main reason for restricting the improvement of LED display clarity is uniformity rather than physical pixel pitch

With the development of LED display technology to today, uniformity has become the most important indicator to measure the pros and cons of the display. It is often said that the LED display "a little bit brilliant, the piece is brilliant" is an image metaphor for the serious unevenness between pixels and modules. The professional point is "dust effect" and "mosaic phenomenon".

The root causes of the inhomogeneity are: the inconsistency of LED performance parameters; the lack of assembly accuracy in the production and installation process; the consistency of electrical parameters of other electronic components is not sufficient; the module and PCB design are not standardized.

Among them, "the inconsistency of LED performance parameters" is the main cause. The inconsistencies of these performance parameters mainly include: inconsistent light intensity, inconsistent optical axis, inconsistent color coordinates, inconsistent light intensity distribution curves of various primary colors, and inconsistent attenuation characteristics. How to solve the inconsistency of LED performance parameters, there are two main technical approaches in the industry: First, through the further subdivision of LED specifications, improve the consistency of LED performance; Second, improve the display through subsequent correction Uniformity. Subsequent corrections have evolved from early module corrections and module corrections to today's point-by-point corrections. The correction technique is developed from simple light intensity correction to light intensity + color coordinate correction.

However, we believe that subsequent corrections are not omnipotent. Among them, the inconsistent optical axes, inconsistent light intensity distribution curves, inconsistent attenuation characteristics, poor assembly accuracy, and irregular design are not eliminated by subsequent corrections. Even such subsequent corrections will result in optical axes, attenuation, and assembly accuracy. The inconsistency is getting worse.

Therefore, through the practice of our conclusions: the follow-up correction is only the treatment of the table, and the LED parameter subdivision is the root cause, is the future mainstream of the LED display industry.

When it comes to the relationship between display uniformity and sharpness, there is often a misunderstanding in the industry that replaces sharpness with resolution. In fact, the display resolution is a subjective feeling of the human eye on the display resolution, uniformity (signal-to-noise ratio), brightness, contrast and other factors. Simply narrowing the physical pixel pitch to improve the resolution, while ignoring the uniformity, there is no doubt about improving the definition. Imagine a display with a serious "dust effect" and "mosaic phenomenon". Even if its physical pixel pitch is small and the resolution is high, it is impossible to obtain a good image sharpness.

Therefore, in a sense, the main reason for restricting the improvement of the definition of LED display screens is "uniformity" rather than "physical pixel pitch".

How to choose the LED display package device LED lamp beads affect the display pixel out of control

· The main reason for the loss of control panel pixels is LED failure

·Electrostatic discharge is the biggest cause of failure

There are many reasons why the display pixels are out of control. The most important reason is "LED failure".

The main cause of LED failure can be divided into two aspects: one is the poor quality of the LED itself; the other is the improper use method. Through analysis we sum up the LED failure mode and the correspondence between the above two main causes.

As mentioned above, the failure of many LEDs is usually not found in the routine inspection of LEDs. In addition to being improperly used due to electrostatic discharge, high current (causing excessive junction temperature), external strength, etc., many LED failures are caused by high temperature, low temperature, rapid temperature change or other harsh conditions, due to LED chips , epoxy resin, and brackets. The difference in thermal expansion coefficient of materials such as inner leads, solid crystal adhesives, and PPA cups is caused by the difference in internal stress. Therefore, quality inspection of LEDs is a very complicated task.

Furthermore, for GaN-based LEDs, electrostatic discharge is the biggest cause of failure. The mechanism of electrostatic discharge leading to LED failure is very complicated. Equipment, tools, utensils and human body may have static electricity and discharge it. This static electricity is as low as several hundred volts, high is tens of thousands of volts, and discharge time is in the nanosecond level. . The blue-green tube failure that occurs during the production, installation, and use of the display screen is often caused by the breakdown of the LED-PN junction by electrostatic discharge. The International Electrostatic Association strictly stipulates the standard electrostatic discharge mode, which is mainly divided into human discharge mode (HBM) and machine discharge mode (MM). China's electrostatic discharge sensitivity (ESDS) for devices is divided into three levels (human body mode): 1 to 0 to 1999V; 2 to 2000 to 3999V; and 3 to 4000V. Under normal circumstances, the electrostatic discharge sensitivity of LEDs is between several hundred volts and tens of thousands of volts in human mode, and only tens of volts to five hundred volts in machine mode. Due to the complicated production process of the LED display, the electrostatic discharge is insurmountable. Therefore, the electrostatic discharge sensitivity of the LED should be 2 or above (human body mode), and the electrostatic protection must pass through the whole process of production.

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