Table of Contents
Reference Documents
Below are some important concepts and testing methods that get from below documents.
GB/T 43770-2024 which was issued by National Standardization Administration Committee of China
SJ/T 11281-2017 which was issued by Ministry of Industry and Information Technology of the People’s Republic of China
T/COEMA 110S-2021 which was issued by China Optics and Optoelectronics Industry Association
Pixel pitch
Pixel is the smallest lighting unit which is composed of Red, Green, and Blue lamp. Pixel pitch means the distance of the adjoining pixels. If the horizontal pixel pitch is the same as the vertical pixel pitch, then we can use Px.xx to stand for the pixel pitch of the LED display. If the horizontal pixel pitch is different from the vertical pixel pitch, then we need to list the pixel pitch separately like Px:3.91mm, Py:7.82mm.
1:Large pixel pitch displays
Led screen that the pixel pitch is bigger than 8.00mm
2:middle pixel pitch displays
Led screen that the pixel pitch is among 2.50mm – 8.00mm
3:fine pixel pitch displays
Led screen that the pixel pitch is among 1.00mm – 2.50mm
4:mini pixel pitch displays
Led screen that the pixel pitch is among 0.30mm – 1.00mm
5:Micro pixel pitch displays
Led screen that the pixel pitch is smaller or equate to 0.30mm
Scan rate and time-multiplexing IC
In the early era of led display, it does not have specific IC for led display, hence for every led lamp it would need a IC to control the power supplier( so that the led lamp can light up in sequence to create a image on the screen) . When the pixel pitch is big, it has enough space to place the IC, but when pixel pitch become smaller, it would need a lot more IC hence it would be hard to place the IC. For example,
For a pixel pitch 10.4mm led display, it would need 1000/10.4*1000/10.4*3/16 = 1728pcs IC.
For a pixel pitch 5.2mm led display, it would need 1000/5.2*1000/5.2*3/16 = 6912pcs IC.
In order to make smaller pixel pitch, time-multiplexing IC is invented. With the time-multiplexing IC, each lead of the IC can power several led lamps separately. For example, if the led display is scan rate 8, then every lead of the IC would power this 8 led lamps in a loop. At first time, the first row led lamp would light up, at second time, the second row led lamp would light up…
Greyscale
Greyscale is the ability to show how many grades the led display has from darkness to the brightness. The visual effect of the led display is highly determined by the greyscale ability. If the led display has a low greyscale, it would uneven gradient part during different color areas. Now most of the IC is PMW IC, Greyscale is determined by the GCLK. For more details you can check this article.
The frequency of the display content be showed on the led display in a second, the unit is Hz.
Refresh rate is related to greyscale
In this article, you can have a deeper understanding of the refresh rate.
Refresh rate
Refresh rate means the frequency of the display content be showed on the led display in a second, the unit is Hz. Normally the higher the refresh rate of the led display, less flickering and more stable visual effect the led display would have. You might be curious why in LCD display, normally the refresh rate is 60hz, and now in LED display, the refresh rate need 1920hz, 3840hz or even 7680hz. You can read more details of this in this article. The greyscale , scan rate, and refresh rate are all determined by the IC.
Brightness
The measure of light emitted per unit area, unit is nit or cd/m2. The brightness of the led display usually refer to the white balanced brightness at the vertical(normal) direction (Red light:Green light : Blue light = 3:6:1). We can change the brightness of the led display through different method you can check this article.
Contrast rate
testing method of Max Contrast Ratio:
Testing condition:
- For indoor led display, the Normal direction’s illuminance of screen surface should be 10 x (1+-10%) lx;
- For indoor led display, the Normal direction’s illuminance of screen surface should be 5000 x (1+-10%) lx;
- Color meter should capture at least 16 pixels during testing
Testing procedure:
- Measure the MAX brightness of the led display Lmaxand the background brightness (led display not light up) LD
- Calculate the Max contrast ratio
C = (Lmax – LD ) / LD
(By doing what the standard required, it need a lab condition, as it is hard to create 10lx environment, but we did it before, and the contract rate would be bigger than 20000:1 )
Color gamut coverage ratio
The ability of what color the led display can show. As all the color of the led display is mixed by Red, green and blue light. Hence the color coordinates of the red, green, and blue determine the color scope the led display can show.
In this article, you can know more details of the Color gamut of the led display
SMD, GOB, COB
SMD means Surface mount Device, it is a led lamp package method, we call the led display that using SMD led lamp SMD led display.
GOB means Glue on board, it is a technology that used in SMD led display. As the SMD led lamp’s connecting pad is expose to air, which would be oxidiation, and the led lamp is also easy to be scratched off the board.
COB means chip on boards. You can find more details about SMD, GOB, and COB in the article.
Viewing Angle
We change the observation direction of the led display until the observed brightness becomes half of brightness of the vertical direction. And the two horizontal observation direction angle is the horizontal viewing angle. So does the vertical viewing angle.
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