Detailed explanation of LED & LED display knowledge
In recent years, with the holding of Beijing Olympic Games, Shanghai World Expo and Guangzhou Asian Games, the figure of LED display screen can be seen everywhere. LED display screen can display changing numbers, words, graphics and images; It can be used not only in indoor environment, but also in outdoor environment. It has incomparable advantages over projectors, TV walls and LCD screens.
LED has been widely valued and developed rapidly, which is inseparable from its own advantages. These advantages can be summarized as follows: high brightness, low working voltage, low power consumption, miniaturization, long service life, impact resistance and stable performance. The development prospect of LED is extremely broad. As the industry leader, FBelec company, an old 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 panchromatic.
1、 Type of LED display:
1. Classification by color
Single primary color display screen: single red or single green; Dual color display screen: red and green dual primary colors, 256 gray levels, and can display 65536 colors; Full color display: red, green and blue. The full-color display with 256 gray levels can display more than 16 million colors.
2. Classification according to constituent pixel units
Digital display screen: the display pixel is 7-segment nixie tube, which is suitable for making clock screen, interest rate screen, etc;
Graphic display screen: the display pixel is a dot matrix module, which is suitable for playing text and image information;
Video display screen: the display pixel is composed of many light-emitting diodes, which can display video, animation and other video files.
3. Classification according to use location
Indoor display screen: small luminous points, dense pixel spacing, suitable for close viewing;
Semi outdoor display screen: between indoor and outdoor, it is not rain proof, and is suitable for information guidance on the lintel;
Outdoor display screen: large luminous point, large pixel spacing and high brightness. It can work in the sun. It has windproof, rainproof and waterproof functions, and is suitable for long-distance viewing.
4. According to the driving mode, there are static, horizontal scrolling, vertical scrolling and page turning display.
2、 Types, advantages and disadvantages of LED for display screen
According to the classification of the display screen, the pixel LEDs used can also be divided into the following types:
1. Lattice module
Advantages: low cost, mature processing technology and stable quality; Disadvantages: the consistency of brightness and color is not easy to control, and it is easy to appear masseg phenomenon;
2. In line lamp
Advantages: the color consistency is easy to control, and the pixel spacing can be adjusted and combined freely according to needs; Disadvantages: the color mixing effect of red, green and blue is poor, the angle is not large, it is difficult to control the consistency of the angle, and it is easy to be uneven in processing, and it is easy to be misplaced up, down, left and right;
3. Patch
Advantages: the display color, color mixing effect and angle consistency are the best; Disadvantages: high cost of packaging and processing;
3、 Technical requirements for LED packaging for display screen
Different display screens of different specifications will be used in different application positions, and different display screens need LED devices with different technical requirements. What are the technical requirements of LED for display screen? It is explained one by one according to different classifications:
1. Patch LED for indoor display screen
The patch LED used for indoor display screen is divided into "three in one" and "three in one". The former is mostly used in fields with relatively low cost and low display requirements, while the latter has better display effect and relatively high cost. The following mainly describes "three in one";
(1). Brightness:
The first thing to consider is the appropriate proportion matching of product brightness. At present, the red, green and blue brightness matching of most full-color displays is based on the proportion of 3:6:1 (that is, the red brightness accounts for 30%, green accounts for 60% and blue accounts for 10% in a pixel); Generally speaking, packaging plants and upstream chip manufacturers almost test products according to 20mA, but when they are really applied to the display screen, it is almost not this current that drives the LED lamp. Generally speaking, the three kinds of red, green and blue LEDs have different chip materials, and their heating, luminescence and brightness attenuation are also disproportionate in practical use, Generally speaking, the red attenuation ratio is smaller and the blue-green attenuation is larger. Therefore, in order to ensure the relatively long service life of the display screen, the general designer will lower the blue-green driving current than the red; For example, if red is driven by 18ma, green is driven by 15mA and blue is driven by 12mA, according to the IV if relationship of LED chip:
We can roughly calculate that the relationship between the actual LED brightness and 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 grading is to make the display screen not allow the naked eye to see the brightness difference. Generally speaking, the brightness difference that the human eye can sensitively distinguish is 30%. After deducting the equipment test error and installation mechanism error, it is better to design the light splitting according to 10% ~ 20%.
(2). Color:
According to the optical effect, the white light is decomposed into a color spectrum with gradual transition of multiple colors after passing through the prism. The colors are red, orange, yellow, green, blue, blue and purple, which is the visible spectrum. Human eyes are most sensitive to red, green and blue. Human eyes are like a three-color receiver system. Most colors can be synthesized by red, green and blue in different proportions. Similarly, most monochromatic light can also be decomposed into 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. No primary color can be combined with the other two colors. Red, green and blue are the three primary colors, and the color range of these three colors is the most extensive. The three primary colors of red, green and blue are added in different proportions to synthesize the mixed color, which is called additive mixed color. Three primary colors are three colors that are independent of each other, and none of them can be mixed by other two colors.
The color obtained by adding the three primary colors with different proportions is called additive color mixing. The law is:
Red + Green = yellow
Red + blue = Purple
Blue + Green = blue
Red + Blue + Green = white
The best color matching of LED for display screen is: red 620-630nm, green 520-530nm and blue 465-475nm. Of course, this range can be reduced according to actual needs. For example, red takes 3nm as the first gear and blue-green takes 2.5nm as the first gear.
Angle: in fact, for the angle, the bigger the better, but more importantly, the angle is not only large, but also the angle curve should be full and smooth, and the red, green and blue should coincide uniformly. Otherwise, after the display screen is completed, dark areas will be displayed in some positions, or a certain color is particularly bright or dark;
(3). Electrical parameters
The electrical parameters of LED are mainly reflected in forward voltage (VF), reverse current (IR) and anti-static (ESD). Generally, the display screen is driven by constant current of 5V DC power supply. Therefore, the VF of LED generally does not require too high consistency, as long as it is controlled within a reasonable range (generally red 1.8-2.2v, blue-green 3.0-3.4v); Generally speaking, the larger the ESD, the better. Because ESD is everywhere, the larger the ESD of LED, the less likely it is to cause problems in the processing of display screen; Reverse current requirements VR = 5V, IR ≤ 10uA
Oval direct plug led for outdoor display
The LED for outdoor display screen generally uses the straight plug-in lamp with elliptical structure. Compared with the LED for indoor display screen, the luminous angle of outdoor elliptical lamp is mainly divided into horizontal and vertical angles. Generally, for outdoor display screen, the horizontal visual range is relatively large, and the vertical visual range is relatively small;
Generally speaking, it is better for the LED of outdoor display screen to have a transverse angle of about 110 degrees and a longitudinal angle of about 50 degrees. Due to the influence of many factors on the angle of direct plug-in lamp, it is mainly reflected in:
(1) Packaging appearance shape of LED;
(2) Bowl and cup structure of support;
(3) Wafer and its structure;
(4) Refractive index of packaging glue;
(5) Consistency of material quality;
(6) Packaging process (i.e. the luminous height position of the wafer);
Therefore, the angle of LED for outdoor display screen is not easy to grasp. It not only needs good design, but also has a good level of process design and quality control.
FBelec is committed to the electronic engineering series of LED display screen manufacturers And provide: indoor, outdoor, industrial, monochrome, color, full-color and other types of LED LCD solutions
