Discussing the problem of LED street light decay from the perspective of heat dissipation technology

　　The serious light decay problem of LED street lamps needs to be solved from the fundamental point of LED heat dissipation technology . At present, the growth rate of LED street lamps in China is higher than that of other countries. According to statistics, it is predicted that China will still rank first in the global market in 2013. The "10 Cities, 10,000 Lamps" semiconductor lighting application project pilot policy approved by the Ministry of Science and Technology of China last year is a model of economic development that creates market demand through central policies, but the first-line response of manufacturers to the actual case is not as expected.

　　The gap between policy and market, in addition to the fact that LED standards have not yet been fully standardized for manufacturers to follow, another potential technical problem is "LED street lamps have serious light decay", which has resulted in LED street lamps that have been installed for less than a year being unable to pass the certification and acceptance of the user unit. The aforementioned LED standard specification unified formulation issue may be finalized in the near future. As for "LED street lamps have serious light decay", it needs to be solved from the fundamentals of LED heat dissipation technology.

　　Discussion on the causes of LED street light failure

　　Temperature is actually the key issue of LED street light decay, but LED street lights are stuck at this stage. Since the luminous power of LED street lights is greater than that of household lamps, manufacturers have spent a lot of effort on the design of heat dissipation substrate fins and heat dissipation modules. After assembly, the heat dissipation module of the lamp needs to be painted to prevent weather erosion. Unexpectedly, the external protective paint seals back the heat of the heat dissipation module, resulting in poor heat dissipation and LED epitaxial light decay.

　　The heat energy of LED epitaxial luminescence belongs to concentrated heat energy in a small range. When it is used in high-power street lamps, the power input is also large, and the interface temperature of LED is quite high. When the street lamp is working for a long time, if the heat dissipation module cannot effectively dissipate heat, it will affect the service life and luminous performance of LED. For example, the serious light decay of LED street lamps is caused by these factors. LED street lamps are used outdoors and there are interference factors of environmental climate, so most manufacturers protect the outer shell of LED street lamp radiator with anodizing treatment or spray paint to avoid corrosion by acid and alkali substances. The life of anodizing is not long, and it will still oxidize and discolor after a while. If it needs to be dismantled and reworked, it will not only be time-consuming and labor-intensive, but also increase maintenance costs; paint protection has a lower cost and good protection effect, but generally paint has no heat dissipation function, and the paint body itself will form a barrier effect, which is equivalent to increasing the thermal impedance of the LED street lamp radiator. Not only does it not help, but it also blocks the heat energy in the radiator, reducing the luminous power of the LED, and finally leading to serious light decay. The above serious problems have always existed in the LED lighting industry, and are almost the main reason why public engineering LED street lights cannot pass the acceptance of purchasing units.

The principle of virtual pixel display

　　The virtual pixel LED display screen uses software algorithms to control the light-emitting tubes and enable the light-emitting tubes to participate in the imaging of multiple adjacent pixels. The virtual screen uses fewer tubes to achieve a higher resolution, which can increase the pixel resolution of the LED display screen by 4 times.
 

　　Definition of Virtual Pixel Display

　　The red, green, and blue display components of each point in the display unit are evenly distributed to match the color mixing effect of the pixel; the representative color of the virtual display point is composed of the mixed colors of adjacent red, green, and blue pixels. The points of virtual pixels are scattered, and the points of real pixels are condensed. The light-emitting points of virtual pixels are between the lamps, and the light-emitting points of real pixels are on the lamps.

　　The realization method of virtual pixels 

　　is to design the module according to 2 red, 1 green and 1 blue. Then the conversion relationship between real points and virtual points is: m=2m-1, m is the virtual point, n is the real point. For example, when m=3, the real point pixel is 3×5 dot matrix, and the virtual pixel is 5×9 dot matrix. From this we can get that if n is the number of row LED tubes and m is the number of column LED tubes, then the pixel points displayed by the real pixel are m×n, and the pixel points displayed by the virtual pixel are (2n-1)×(2m-1). In this way, when m and n are large enough, it is approximately equal to 2n×2m, that is, 4m×n, so it is 4 times the real pixel.
 

Figure 1 Principle of virtual pixel implementation

 
Figure 2 Module of virtual pixel display screen

　　Analyzing the module in Figure 2, taking the green light as an example, there are 16 lights in the row and 8 lights in the column. Therefore, the actual pixel number is 16×8. Because of the use of virtual pixel technology, the actual pixel number is (16×2)×(8×2), which is increased by 4 times.

　　　　Analysis of the process of realizing LED display screen virtual technology

Figure 4 LED display virtual technology display process