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How to correctly understand the main performance indicators of LED display wall
Since 1998, after five years, under the LED Display Special Committee (now the China Optical Association LED Display Branch) organization efforts, "LED display test method" industry standard (hereinafter referred to as "Standard") will be released soon. Therefore, correctly guiding users to understand the performance indicators of LED display screens is of great significance to the standard LED display market. In order to better implement the standards, the following suggestions are made.
Maximum brightness
 
In the industry "Standards" discussed at the end of last year, there is no clear characteristic requirement for the important performance of "maximum brightness", which is in line with GB/T1.2-2002. In the "Numerical Work Guide Part 2: Determination of the Content of Normative Technical Elements in the Standard", "5.4.3 Values ​​Determined by the Supplier" refers to: "If the product is allowed to be diversified, then certain products The characteristic values ​​do not have to be specified (although these characteristics have a significant impact on the performance of the product). Because the environment in which the LED display is used varies widely, the illumination (which is what the average person calls the ambient brightness) is different, so "for most complex products, a performance data is provided by the supplier as long as the corresponding test method is specified in the standard. The (product information) list is better than the specific performance requirements given in the standard." These are in line with international standards, but this also creates unrealistic comparisons in bidding, and users do not understand this, resulting in the “maximum brightness” required in many bids is often much higher than the actual needs. Therefore, it is recommended that in order to guide users to correctly understand the "maximum brightness" of the LED display, it is necessary for the industry to give a guide: in some occasions, under the different illumination environment, what is the brightness of the LED display? Can meet the requirements.
2. Primary color dominant wavelength error
 
Changing the primary color wavelength error index from the "primary color wavelength error" to the "primary color primary wavelength error" is more indicative of what this LED reflects in the LED display. The dominant wavelength of color is equivalent to the hue of the color observed by the human eye. It is a psychological quantity and an attribute that distinguishes colors from each other. And the performance requirements stipulated by this industry standard, literally, users can not understand that it is an indicator reflecting the color uniformity of LED display. So, is it to guide the user to understand the term first, and then understand this indicator? Or do you first understand and understand the LED display from the customer's point of view, and then give you the easy-to-understand performance characteristics that users can understand? As mentioned in the above-mentioned GB/T1.2-2002 (Standardization of the content of normative technical elements in the standardization work guide Part 2 standard), one of the principles for the formulation of product standards is the “performance principle”: “when possible Requirements should be expressed by performance characteristics, without design and description of features, this method leaves the greatest room for technological development. "Primary color primary wavelength error" is such a design requirement, because of "color uniformity" Instead, there is no LED that defines the wavelength. For the user, as long as you ensure that the color of the LED display is uniform, regardless of the technical means you use, it is as large as possible for the development of technology. There is room for this, which is greatly beneficial to the development of the industry.
 
3. Duty cycle
 
Just like the "performance principle" mentioned above, "if possible, the requirements should be expressed by performance characteristics, without design and description of the characteristics, this method leaves the greatest room for technological development." We believe that "duty cycle" is purely a design technology requirement and should not be used as a performance indicator for LED display product standards; everyone knows that there is a user who cares about the display duty cycle of the display, they care The effect of the display is not the realization of our technology; why should we create such technical barriers and limit the technological development of the industry?
 
4. Refresh frequency
 
From the measurement method of "Standard", it seems that the problem that the user really cares about is ignored. It also does not take into account the different driving ICs, driving circuits and methods used by various manufacturers, which makes the testing difficult. For example, the full color screen bidding of the Shenzhen Stadium, in the expert sample test, the test of this indicator brings many problems. The "refresh frequency" frame shows the reciprocal of the required time, and the display screen is used as a light source, which is the blinking frequency of the light source. We can directly test the flashing frequency of the display's light source with an instrument similar to the “light-sensing frequency meter” to reflect this indicator. We have done this test using an oscilloscope to measure the LED drive current waveform of any color to determine the "refresh frequency", measured 200Hz in the white field; in the low gray level such as 3 gray scale, the measured frequency is up to More than ten k Hz, and measured with PR-650 spectrometer; whether in the white field, or in the gray level of 200, 100, 50, the measured source flashing frequency is 200 Hz.
 
The above points are only a simple description of the characteristics of several LED displays, and there are many "working life", "average time between failures" encountered in bidding, etc. No test method can be shorter. It is confirmed within the time that the LED display meets the requirements of stability, reliability or longevity; these requirements should not be specified. The producer can make a guarantee, but it cannot replace the requirement. It is a business concept, a contract concept, not a technical concept. Industry associations should have a clear statement about this, which will be very beneficial to users, producers and the entire industry.
 
For how to guide users to correctly understand the product of a complex system such as LED display, it is necessary for the industry association to engage in more LED display technology forums. It is more practical to analyze this product from the user's point of view and guide users to correctly understand the LED display. .
 
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