LED industry secrets

In recent years, with the holding of the Beijing Olympic Games, Shanghai World Expo, and Guangzhou Asian Games, LED display screens can be seen everywhere. LED display screens can display changing numbers, text, graphics and images; they can be used not only in indoor environments but also in outdoor environments, and have advantages that projectors, TV walls, and LCD screens cannot match. The
widespread attention and rapid development of LED are inseparable from its own advantages. These advantages can be summarized as: high brightness, low operating voltage, low power consumption, miniaturization, long life, impact resistance and stable performance. The development prospects of LED are extremely broad. As the industry leader, Shanghai Xingma Electronics, a long-established enterprise, plays a key role in the early development of the industry. At present, LED is developing towards higher brightness, higher weather resistance, higher luminous density, higher luminous uniformity, reliability, and full color.
1. Types of Shanghai Xingma LED display screens:
1. Classification by color
Single-color display screen: single red or single green; dual-color display screen: dual-color red and green, 256 grayscale, can display 65536 colors; full-color display screen: red, green, blue three primary colors, 256 grayscale full-color display screen can display more than 16 million colors.
2. Classification by pixel unit
Digital display screen: display pixels are 7-segment digital tubes, suitable for making clock screens, interest rate screens, etc.;
graphic display screen: display pixels are dot matrix modules, suitable for playing text and image information; video
display screen: display pixels are composed of many light-emitting diodes, which can display various video files such as videos and animations.
3. Classification by use location
Indoor display screen: small light point, dense pixel spacing, suitable for close viewing;
semi-outdoor display screen: between indoor and outdoor, not rainproof, suitable for information guidance on door lintels, etc.;
outdoor display screen: large light point, large pixel spacing, high brightness, can work in the sun, with windproof, rainproof and waterproof functions, suitable for long-distance viewing.
4. According to the driving mode, there are static, horizontal scrolling, vertical scrolling and page turning display.
2. Types and advantages and disadvantages of LEDs used in Xingma display screens
According to the classification of display screens, the pixel LEDs used can also be divided into the following types:
1. Dot matrix module
Advantages: low cost, mature processing technology, stable quality; Disadvantages: brightness and color consistency are not easy to control, and mosaic phenomenon is easy to appear;
2. Direct plug-in lamp
Advantages: color consistency is relatively easy to control, and the pixel spacing can be freely adjusted and combined according to needs; Disadvantages: The red, green and blue color mixing effect is not good, the angle is not large, and it is difficult to control the angle consistency. It is easy to appear uneven in processing, and it is easy to misalign up and down;
3. SMD
Advantages: display color, color mixing effect, angle consistency, etc. are all the best; Disadvantages: packaging, processing, etc. are costly;
3. Technical requirements for LED packaging for Xingma display screens
Different application locations will use display screens of different specifications, and different display screens require LED devices with different technical requirements. So what are the technical requirements for LEDs used in display screens? The following is an explanation of each category:
1. SMD LED for indoor display screens.
SMD LED for indoor display screens can be divided into "three-in-one" and "three-in-one". The former is mostly used in relatively low-cost fields with low display requirements, while the latter has better display effects and relatively higher costs. The following mainly explains the "three-in-one";
1. Brightness:
The first thing to consider is the appropriate ratio of product brightness. At present, the red, green and blue brightness of most full-color display screens are matched according to the ratio of 3:6:1 (that is, the red brightness accounts for 30%, the green accounts for 60%, and the blue accounts for 10% in a pixel). Generally speaking, packaging factories and upstream chip manufacturers almost all test products according to 20mA, but when it is actually applied to display screens, almost none of them drive LED lights with this current. Generally speaking, the three types of LEDs, red, green and blue, are made of different chip materials, and their heat generation, light emission and brightness attenuation in actual use are also disproportionate. Generally speaking, the red attenuation ratio is smaller, and the blue-green attenuation is larger. Therefore, in order to ensure that the service life of the display screen is relatively long, the general designer will make the blue-green driving current lower than the red. For example: if the red is driven at 18mA, the green is driven at 15mA, and the blue is driven at 12mA, according to the IV-If relationship of the LED chip:
we can roughly deduce that the actual required LED brightness, the relationship between red, green and blue is:
R:3÷90%
G:6÷75%
B: 1÷60%
At the same time, the brightness should be graded. The purpose of the graded display is to make the display screen not visible to the naked eye. Generally speaking, the brightness difference that the human eye can distinguish is 30%. After deducting the test error of the equipment and the error of the installation mechanism, it is better to design the light splitting according to 10%~20%.
2. Color:
According to the optical effect, white light is decomposed into a variety of colors after passing through the prism. The colors are red, orange, yellow, green, cyan, blue, and purple. This is the visible spectrum. Among them, the human eye is most sensitive to red, green, and blue. The human eye is like a system of three-color receivers. Most colors can be synthesized by red, green, and blue in different proportions. Similarly, most monochromatic light can also be decomposed into three colors of red, green, and blue. This is
the most basic principle of colorimetry, that is, the principle of three primary colors. The three primary colors are independent of each other, and any primary color cannot be synthesized by the other two colors. Red, green, and blue are the three primary colors, and the color range synthesized by these three colors is the widest. The addition of the three primary colors of red, green, and blue in different proportions is called additive color mixing. The three primary colors are three colors that are independent of each other, and any color cannot be produced by mixing the other two colors.
The addition of the three primary colors in different proportions is called additive color mixing. The rule is:
red + green = yellow
red + blue = purple
blue + green = cyan
red + blue + green = white
The best color combination for LED display is: red 620-630nm, green 520-530nm, blue 465-475nm. Of course, this range can be narrowed according to actual needs, such as 3nm for red and 2.5nm for blue and green.
Angle: Actually, the bigger the angle, the better. But more importantly, the angle is not just big. The angle curve should be full and smooth, and the red, green and blue should overlap. Otherwise, after the display is completed, some positions will show dark areas, or one color will be particularly bright or dark.
3. Electrical parameters
The electrical parameters of LED are mainly reflected in the forward voltage (vf), reverse current (Ir) and anti-static (ESD). Generally, the display screen adopts a 5V DC power supply with a constant current drive. Therefore, the Vf of LED is generally not required to be too consistent, as long as it is controlled within a reasonable range (generally 1.8-2.2V for red, 3.0-3.4V for blue and green). Generally, the larger the ESD, the better. Because ESD is everywhere, the larger the ESD of LED, the less likely it is to have problems in the processing of the display screen. The reverse current requires Vr=5v, Ir≦10uA.
Elliptical direct-plug LED for outdoor display screen
LEDs for outdoor displays are generally elliptical plug-in lamps. Compared with LEDs for indoor displays, outdoor elliptical lamps mainly have horizontal and vertical angles. Generally, for outdoor displays, the horizontal visible range is relatively large, while the vertical visible range is relatively small.
Generally speaking, the horizontal angle of LEDs for outdoor displays is about 110 degrees, and the vertical angle is about 50 degrees. The angle of plug-in lamps is affected by many factors, mainly:
(1) the appearance of the LED package;
(2) the bowl structure of the bracket;
(3) the chip and its own structure;
(4) the refractive index of the packaging glue;
(5) the consistency of material quality;
(6) the packaging process (i.e. the luminous height position of the chip).
Therefore, the angle of LEDs for outdoor displays is more difficult to control, which requires not only good design, but also good process design and quality control.
With the continuous improvement of technology, the requirements for display screens will become higher and higher, and of course the requirements for LED packaging technology will be equally high.