Briefly describe how LEDs dissipate heat

Theoretically, the total electro-optical conversion efficiency of LED is about 54%. At the current level of LED technology development, the highest electro-optical conversion efficiency reported in reports is less than half of the theoretical value, and more than 1/4 of its theoretical value in practical applications! The remaining electrical energy will be released in the form of thermal energy, which is why LEDs generate heat. If the heat is accumulated too much, it will cause giant harm to the LED, such as reduced light efficiency, color temperature drift, and shortened life. Therefore, in order to ensure the stability of the use of LED lamps, people will use various methods to dissipate heat for the LED chip.
 
      There are many ways to actually direct this heat out of the chip to the outside air. Specifically, the heat generated by the LED chip comes out of its metal heat sink, passes through the solder to the PCB of the aluminum substrate, and then passes through the thermally conductive adhesive to the aluminum heat sink. Therefore, the heat dissipation of LED lamps actually includes two parts: heat conduction and heat dissipation. Before connecting the LEDs to the heat sink, they must first be soldered into the circuit, because these LEDs must first be connected in series and parallel, and they must also be connected to the constant current source on the circuit. The easiest way is to solder them directly to ordinary printed boards. Aluminium substrates are currently used in almost all LED lamps. The copper foil of the circuit on the aluminum substrate must have a sufficient thickness and width in order to be conductive and thermally conductive, and its thickness is between 35 μm and 280 μm. It is best to cover the entire substrate as wide as possible to transfer heat. On the circuit of the substrate, heat can be transferred to the aluminum plate, but unfortunately, this aluminum plate is often not the final heat sink, and it is usually connected to the real heat sink. The easiest way is to connect the heat sink with rivets or screws. However, this method often forms an air gap, and the thermal resistance generated by a small air gap is dozens of times greater than other thermal resistances. Because the thermal conductivity of air is 0.023W / m • k. Therefore, it is necessary to apply thermal conductive glue to fill the gap. The thermal conductivity of general thermal silica gel is about 1-2W / m • k. And the selected thermal adhesive must have certain fluidity and cohesiveness, because the thermally conductive adhesive with poor flow is easy to produce air gap due to uneven application, and the effect may be worse than not used, and the adhesiveness is mainly fixed Aluminum substrate and aluminum heat sink