Analyze the reasons why LED generates heat

Considering the comprehensive current injection efficiency, radiative luminescence quantum efficiency, chip external light extraction efficiency, etc., only about 30-40% of the input electrical energy is converted into light energy, and the remaining 60-70% of the energy is mainly converted into heat energy in the form of lattice vibrations occurring by non-radiative recombination.

The increase in chip temperature will enhance non-radiative recombination and further weaken the luminous efficiency. Because people subjectively believe that high-power LEDs do not generate heat, but in fact they do. A lot of heat, so much so that problems occur during use. In addition, many people who use high-power LEDs for the first time do not know how to effectively solve the heat problem, making product reliability a major issue. So, does LED generate heat? How much heat can it generate? How much heat does LED generate?

LED在正向电压下，电子从电源获得能量，在电场的驱动下，克服PN结的电场，由N区跃迁到P区，这些电子与P区的空穴发生复合。由于漂移到P区的自由电子具有高于P区价电子的能量，复合时电子回到低能量态，多余的能量以光子的形式放出。发出光子的波长与能量差Eg相关。可见，发光区主要在PN结附近，发光是由于电子与空穴复合释放能量的结果。一隻半导体二极体，电子在进入半导体区到离开半导体区的全部路程中，都会遇到电阻。简单地从原理上看，半导体二极体的物理结构简单地从原理上看，半导体二极体的物理结构源负极发出的电子和回到正极的电子数是相等的。普通的二极体，在发生电子-空穴对的复合是，由于能级差Eg的因素，释放的光子光谱不在可见光范围内。

When electrons are traveling inside a diode, they consume power due to the presence of resistance. The power consumed complies with the basic laws of electronics:

P=I2R=I2(RN++RP)+IVTH

Where: RN is the body resistance of the N region

VTH is the turn-on voltage of the PN junction

RP is the body resistance of the P region

The heat generated by the power consumed is:

Q=Pt

Where: t is the time the diode is energized.

In essence, LED is still a semiconductor diode. Therefore, when LED is working in the forward direction, its working process conforms to the above description. The power it consumes is:

PLED=ULED×ILED

Where: ULED is the forward voltage across the LED light source:

ILED is the current flowing through the LED

The consumed electrical power is converted into heat and released:

Q=PLED×t

式中：t为通电时间实际上，电子在P区与空穴复合时释放的能量，并不是由外电源直接提供的，而是由于该电子在N区时，在没有外电场时，它的能级就比P区的价电子能级高出Eg。当它到达P区后，与空穴复合而成为P区的价电子时，它就会释放出这麼多的能量。Eg的大小是由材料本身决定的，与外电场无关。外电源对电子的作用只是推动它做定向移动，并克服PN结的作用。

LED的产热量与光效无关；不存在百分之几的电功率产生光，其余百分之几的电功率产生热的关係。透过对大功率LED热的产生、热阻、结温概念的理解和理论公式的推导及热阻测量，我们可以研究大功率LED的实际封装设计、评估和产品应用。需要说明的是热量管理是在LED产品的发光效率不高的现阶段的关键问题，从根本上提高发光效率以减少热能的产生才是釜底抽薪之举，这需要芯片制造、LED封装及应用产品开发各环节技术的进步。