EN
Causes of LED junction temperature and methods to reduce it
Jul.27.2025
- The use of high-power LED lighting equipment is increasing. The brightness of high-power LEDs is actually proportional to their current. At the same time, the forward current of high-power LEDs changes with temperature. This article introduces the causes of LED junction temperature and methods to reduce it.
- 01
- Causes of LED junction temperature
- A large part of the reason for LED heating is that the added electrical energy is not completely converted into light energy, and some of it is converted into heat energy. The current luminous efficiency of LEDs on the market is about 100 lm/W, and its electro-optical conversion efficiency is still very low, only about 20~30%. That is to say, about 70% of the electrical energy is wasted in the form of heat energy.
- In general, there are two factors that lead to the generation of LED junction temperature. The details are as follows:
- (1) Internal quantum efficiency.
- When holes and electrons recombine, not all photons are generated. This is usually called "current leakage" and is the reason for the reduction of the carrier recombination rate in the PN region. The product of the leakage voltage and current is the dissipated power, which is converted into heat energy. However, this part is not the main component, because the current technology can make the internal photon efficiency of LED close to 90%.
- (2) The external quantum efficiency is only about 30%.
- The main reason is that the photons generated by carrier recombination cannot be completely emitted to the outside of the chip but converted into heat. Although the luminous efficiency of incandescent lamps is only about 15lm/W, it radiates electrical energy in the form of light energy. Although most of the radiated energy is infrared and the luminous efficiency is very low, this eliminates the problem of heat dissipation. The heat dissipation problem of LED has gradually become a research hotspot. The reason is that the life or light decay of LED is directly related to its junction temperature. If the heat dissipation problem is not handled properly, it will directly cause the junction temperature to be too high and the life to be reduced.
- 02
- Methods to reduce the junction temperature of LED
- ① Control the rated input power;
- ② Design a good secondary heat dissipation structure;
- ③ Reduce the thermal resistance between the secondary heat dissipation structure and the LED mounting interface to a minimum;
- ④ Reduce the ambient temperature;
- ⑤ Reduce the thermal resistance of the LED itself.