Positive thinking on how to improve the reliability of LED road lighting

In recent years, under the global environmental protection trend, the LED lighting industry has grown rapidly, and many technology companies have invested in this emerging industry. However, due to the failure to establish and properly regulate the performance standards of LED lighting, a large number of products failed to pass the test and ended up with serious light decay. The main reason is that there is no design theoretical research as a pillar for inspection, which has caused doubts among users and delayed the development of the industry. Thermalking, a supplier of LED lighting solutions, provides important technical indicators and specifications of various components of high-performance LED street lights to lighting systems for reference by the industry.

Regarding the key technology indicators of LED chip and package component luminous efficiency , the key technology of LED chip and package component is the most important. European, American and Japanese manufacturers have already achieved mass production with luminous efficiency exceeding 100~120lm/W, surpassing the traditional most efficient HID light source (luminous efficiency 90~110lm/W), solving the problem of the current LED lamps’ overall luminous efficiency being insufficient ≧45lm/W, meeting the requirements of long road lighting life, low light decay, and average illumination in line with international standards , reaching 25~40Lux specifications and energy saving of 30~60%.

Regarding the key technical indicators of LED luminous efficiency, temperature rise and life specifications, the data published by CREE or Osram LED and other manufacturers are reviewed. The chip PN junction operating temperature Tj < 75~85℃ can ensure a working life of 50,000 hours at a light output efficiency of more than 85%, and the temperature rise from the chip PN junction to its own thermal conductive sheet (Tjs) is ΔT = 6~15℃. In addition, the LED light efficiency is inversely proportional to the operating temperature. Every 10℃ increase will lead to a serious consequence of 3~6% light decay and halving of the life. This is far from the general argument that LEDs can work at 100~125℃ and have a life of more than 100,000 hours, but ignore the idea that the light efficiency has been reduced by 25~30% under this condition.

As for the key technical indicators of the heat transfer and cooling environment temperature of LED street lamp system, the operating temperature of such lamp system shall not be higher than 85-10=75℃; Taiwan LED road lamp specification CNS15233 stipulates that the durability test environment temperature is 50℃, so the temperature rise of street lamp cooling system must be less than ΔT≦25℃. Taking Xinyuansheng Technology's 150W LED street lamp as an example, the temperature rise of the heat transfer and cooling system test is as low as ΔT≦13℃, and its thermal resistance value Tr=0.08℃/W is calculated, while most industry manufacturers design system temperature rise test ΔT≒30~40℃, and its thermal resistance value Tr=0.2~0.26℃/W; under the same conditions, Xinyuansheng Technology's products will have a lifespan twice that of other manufacturers' products and the brightness will increase by more than 15%. In addition, in the test of Xinyuansheng Technology's 350W LED lamp, its cooling system temperature rise can still reach ΔT＝15℃, and the thermal resistance value Tr＝0.04℃/W.

The key technology of heat transfer and heat dissipation of LED street light system is that the heat transfer and heat dissipation methods of electronic equipment are suitable for low power natural heat dissipation methods. At present, for products such as MR16/PAR30 from 1 to 70W, the system temperature rise has reached 30 to 40℃. If the natural heat dissipation method is still used for more than 100W, it is like most products on the market. A large amount of aluminum alloy materials must be used to increase the heat conduction and super large heat exchange area, and the volume and weight are 2 to 30Kg, which not only increases the cost of lamps but also increases the risk of safe hanging of lamp poles and lamps. The law of natural heat dissipation is that the heavier and larger the area of ​​metal material used to reduce the temperature, the better the effect. However, the cost of aluminum alloy materials alone increases by NT$60~200/kg. Some manufacturers claim that heat pipes or loop heat pipes can achieve heat dissipation effects, which only solves the problem of heat conduction. Whether it is a heat pipe or a loop heat pipe, it only has the function of heat conduction and not the function of heat dissipation. If you want to achieve good heat dissipation, you must use an effective heat dissipation area of ​​relative wattage, that is, you must increase a large area of ​​metal materials for heat exchange; otherwise, you must use the active forced heat dissipation method used by high-end high-power products such as industrial-grade high-reliability air conditioners and computer CPUs. The high-efficiency, military-standard small fan has a guaranteed life of 70,000 hours and has an IP65 waterproof and dustproof rating. In addition, with appropriate components such as heat pipes and heat dissipation aluminum fins and reasonable structural design, the temperature rise of the lighting system can be as low as ΔT≦12~15℃ after testing, which is 25℃ lower than the natural heat dissipation method, the life will be increased by 2 times, and the light efficiency and brightness will increase by more than 10~15%.

In terms of the reliability and durability of LED street light systems and the environmental adaptability performance test indicators, the general LED lamp product design does not take into account the dust protection system. Outdoor road lamps must completely prevent sandstorms, colloidal suspended matter, and gravity dust accumulation on the heat dissipation structure to avoid the problem of LED overheating and burning. If the heat dissipation structure is facing the ceiling, dust accumulation will occur, and the heat accumulation cannot be dissipated, which may cause LED light decay and burning. To solve the above problems, the heat dissipation structure can be designed to face the ground. Other salt spray resistance tests, etc., Xinyuansheng Technology's existing products have been tested outdoors for 20,000 hours, and the light decay is less than 10%, and the condition is good. The optical design of trunk road lighting can also meet the world standard, that is, a 10-meter-high lamp pole must evenly illuminate a long road with a horizontal width of 40 meters, solving the difficult optical lens design and meeting the aspect ratio requirement of 1:4. In addition, the core wick technology module has also achieved lightweight, and does not need to rely on the lamp shell as a heat dissipator, so the outer shape design of the lamp body can be arbitrarily changed to achieve the beautiful characteristics of each city.

As a practitioner in the high-tech energy-saving lighting industry, we must recognize that good heat dissipation of lamps includes heat conduction, temperature uniformity, heat exchange and other complex traditional basic hard theories of heat transfer. It is not the so-called LED lamp that is cold light and does not generate heat. There is also a single original or special material such as noble nanotechnology or aerospace technology to seek a solution. When end customers are confused, they must face up to the fact that the performance of LED street lights must be supported by scientific data and theories, with a complete system design method as a guideline and a good process as the basis. Finally, the test report of a third-party impartial unit is used as a basis. In this way, the vicious cycle of light decay and hindering industrial development will not occur again and again. Taiwan Xinyuansheng Technology is willing to share the research results and patented technologies of many years with peers all over the world, including invention patents such as forced heat dissipation, downward heat dissipation, liquid heat dissipation and dozens of new patents, and work together to illuminate the world.

In addition, the development of related technologies is explained: At present, the LED chips and packaging technologies are constantly improving. The Tj can withstand temperatures above 100℃, and the life span can reach more than 50,000Hr... However, the physical properties of silicon crystal materials can never be changed. "The luminous efficiency is inversely proportional to the Tj temperature rise." The higher the Tj temperature rise, the lower the luminous efficiency. (See Attachment 2.Pdf) Cree's labeling is based on Tj=25℃ luminous efficiency set to 100%; when Tj=75℃ luminous efficiency decays to 85%; when Tj=125℃ luminous efficiency decays to 70% (That means a newly manufactured lamp has reached L70, with a light decay of 30%), so light efficiency and life span cannot be confused. LED manufacturers deliberately emphasize that their Tj can work at 125℃ and the life span is 50,000Hr, but they do not remind the lamp factory designers that if Tj=125℃ is used as the parameter, it will immediately cause a 30% light loss. Therefore, the world is currently committed to breaking through the key technology of "heat transfer and heat dissipation". The lower the Tj working temperature, the higher the light efficiency. Under this condition, the longest life span can be achieved, which has the greatest competitiveness.