When the LED is working, the following conditions can make the junction temperature rise to varying degrees.

1、 It has been proved that the limitation of luminous efficiency is the main reason for the rise of LED junction temperature. At present, advanced material growth and component manufacturing processes can convert most of the input electric energy of LED into light radiation energy. However, because LED chip materials have much larger refractive coefficients than surrounding media, a large part of photons (>90%) generated inside the chip can not smoothly overflow the interface, and total reflection is generated between the chip and the media interface, It returns to the inside of the chip and is finally absorbed by the chip material or substrate through multiple internal reflections, and becomes hot in the form of lattice vibration, promoting the junction temperature to rise.

2、 Since the P-N junction cannot be extremely perfect, the injection efficiency of the element will not reach 100%, that is, in addition to the charge (hole) injected into the N area in the P area, the N area will also inject charge (electron) into the P area when the LED is working. Generally, the latter type of charge injection will not produce optoelectric effect, but will be consumed in the form of heating. Even if the useful part of the injected charge does not all become light, some will eventually become heat when combined with impurities or defects in the junction area.

3、 The bad electrode structure of the element, the materials of the window layer substrate or junction area, and the conductive silver glue all have certain resistance values. These resistances are stacked against each other to form the series resistance of the LED element. When the current flows through the P-N junction, it will also flow through these resistors, resulting in Joule heat, which will lead to the rise of chip temperature or junction temperature.