In the current practical application, the problems of high-power LEDs are mainly reflected in the following aspects:
1. Insufficient awareness of LED operating conditions and technicality of power supply, resulting in endless product failures on the power supply.
2. The application concept of the practical road of LED street lamps is unclear. The blind and high-power gas discharge lamps are “comparable†to produce super-power LED street lamps without cost, which makes it difficult to promote unrealistic and expensive street lamp products.
3. Insufficient perception of road lighting requirements, scientific point light source optical light distribution difficulties and neglect of the importance of color temperature in road lighting, easy to cause glare, zebra effect and in the environment of serious air pollution, rain and foggy weather, The phenomenon that the light is not bright enough on the ground.
4. The requirements for road lighting are vague, and the actual use and maintenance are not considered, resulting in direct use of the owner's boycott.
5. Due to the lack of understanding of the working conditions of the LED light source, the light attenuation is severe or even dead.
The discussion of the working environment of the LED light source needs to have the basic knowledge of understanding the LED; the core of the LED is the PN junction. Therefore, it has the IN characteristic of a general PN junction, that is, forward conduction, reverse cutoff, and breakdown characteristics. In addition, it has luminescent properties under certain conditions. At the forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A part of the minority carriers (small children) entering the other area is combined with the majority carriers (multi-sub) to emit light. The current high-power LED luminous efficiency is about 30%, and 70% will be heat energy, which needs to be heat-dissipated. The junction temperature TJ of high-power white LEDs shows the relationship between life and lifetime when the brightness is attenuated by 70%: when TJ=50°C, the life is 90,000 hours, when TJ=80°C, the life is reduced to 34,000 hours, when TJ=115°C Its life expectancy is only 13,300 hours. TJ should propose the maximum allowable junction temperature value TJmax in the heat dissipation design. The actual junction temperature value TJ should be less than or equal to the required TJmax, ie TJ≤TJmax.
The heat balance speed of the heat dissipating material requires attention, and the heat of the light source is not effectively treated, resulting in serious light attenuation. Nowadays, many manufacturers' high-power LED heat sink heat-dissipating shell applications basically adopt different alloy aluminum materials, and their thermal conductivity is different. The heat dissipation rate of some materials is difficult to meet the LED working conditions. The non-negligible aluminum substrate and thermal silica gel, the thermal conduction of the silicone grease material, and the actual life quality of the material used will directly affect the working heat dissipation conditions of the LED. How to reduce the intermediate link, directly contact with the heat sink and close the heat to quickly achieve a balanced heat dissipation, is the direction that needs to be considered in the development of high-quality LED lighting products.
First from material analysis:
Metal heat transfer coefficient table -
Silver 429 copper 401 gold 317 aluminum 237 iron 80 tin 67 lead 34.8
Silver heat transfer coefficient is better, but the disadvantage is that the price is too high, the pure copper heat dissipation effect is second, but it is already very good. However, copper also has disadvantages: high cost, heavy weight, and resistance to corrosion. Therefore, most of the heat sinks are made of light and strong aluminum materials, among which aluminum alloys have the best heat transfer capability, and good air-cooled heat sinks are generally made of aluminum alloy. As for copper, there is also a pure copper radiator on the market. The thermal conductivity of copper is much faster than that of aluminum, but the heat of copper is not as fast as aluminum. Copper can quickly take away heat, but it can't be in a short time. Dissipating its own heat, and the oxidizability of copper is the biggest drawback of copper itself. When copper is in an oxidized state, it will greatly decrease in terms of heat conduction and heat dissipation.
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