LED is called the fourth-generation lighting source or green light source. It has the characteristics of energy saving, environmental protection, long life and small size. It can be widely used in various fields such as indication, display, decoration, backlight, general lighting and city nightscape. In recent years, some developed countries in the world have launched fierce technical competitions around the development of LEDs. Among them, LED heat dissipation has always been an urgent problem to be solved!
According to research data, if the LED chip has a 100% light emission at a junction temperature of 25 degrees, then when the junction temperature rises to 60 degrees, its light emission is only 90%; when the junction temperature is 100 degrees, it drops to 80%; 140 The degree is only 70%. It can be seen that improving heat dissipation and controlling junction temperature are very important things.
In addition, the heat of the LED will cause its spectrum to move; the color temperature increases; the forward current increases (when the power supply is constant voltage); the reverse current also increases; the thermal stress increases; the phosphor epoxy resin ages faster, etc. Various problems, so that the heat dissipation of LED is the most important issue in the design of LED lamps.
How the LED chip junction temperature is generated
The reason why the LED generates heat is that not all the added electrical energy is converted into light energy, but a part of it is converted into heat energy. The LED Light efficiency is currently only 100lm / W, and its electro-optic conversion efficiency is only about 20 ~ 30%. That is to say, about 70% of the electrical energy is turned into thermal energy.
Specifically, the LED junction temperature is caused by two factors.
1. The internal quantum efficiency is not high, that is, when electrons and holes recombine, 100% of photons cannot be generated, which is usually called "current leakage" to reduce the recombination rate of carriers in the PN region. The leakage current multiplied by the voltage is the power of this part, which is converted into heat energy, but this part does not account for the main component, because the internal photon efficiency is now close to 90%.
2. The internally generated photons cannot all be emitted to the outside of the chip and are finally converted into heat. This part is the main reason, because the current external quantum efficiency is only about 30%, and most of them are converted into heat.
Although the light efficiency of incandescent lamps is very low, only about 15lm / W, but it converts almost all electrical energy into light energy and radiates it out, because most of the radiation energy is infrared, so the light efficiency is very low, but it is exempted The problem of heat dissipation.
The heat dissipation of LED is now more and more valued by people. This is because the light decay of LED or its life is directly related to its junction temperature. If the heat dissipation is not good, the junction temperature will be high and the life will be short.
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