Analysis of Led lighting heat dissipation and its solutions

With LED technology received widespread attention as a new generation of lighting technology in recent years, LED power grows and heat dissipation problems is being paid more and more attention. After long time observation, researchers find lumens depreciation and lifespan of LED has direct connection with its junction temperature, which may arise if heat dissipation is bad thus makes lifespan shortened.

Unlike previously used incandescent lamp and fluorescent lamp, though energy loss is big, yet most of the energy is directly dissipated by infrared radiation while light source produce less heat. But for LED, all energy is transformed into heat except partial energy being consumed as visible light . Besides, in recent years, electronic products gradually are developed to higher density and higher integration ones, in which LED products is not exceptional. Therefore, solving LED heat dissipation has currently become the key issue to improve LED performance and develop LED industry.
LED’s causes to dissipate heat:

The reason of LED dissipating heat is the electrical power can’t 100% be changed to light energy, whose part is converted to heat energy. LED’s luminous efficacy currently is only 100 lm/w, among which electro-optic conversion efficiency is only about 20 ~ 30%.That is to say, about 70% of electrical power has been converted to heat energy.

Specifically, the generation of LED junction heat come from two factors:

Internal quantum efficiency is not high, which means, electrons cannot 100% produce photon when compound with holes, usually as a result of “current leakage” lowering compounding ratio on PN area. Leakage current multiplied by the voltage, its calculated value is the power that has been converted into heat, but it does not occupy a main component part, because now the internal efficiency of photon is close to 90%.

Photons produced interiorly cann’t all emit out the chips and thus finally be converted to heat, which part is the main; because efficiency of these named external quantum is only about 30%, most of which is converted into heat.

As previously mentioned, although luminance efficiency of incandescent lamp is very low, only 15 lm/W, but it can mostly convert electrical power into light energy to radiate out. Most radiant energy is infrared, so the luminance efficiency is very low, but can be exempt from the heat dissipation problem.

Solutions to LED heat dissipation:

Solutions to LED heat dissipation mainly come from two aspects: before encapsulation and after encapsulation, which can be understood as LED chip heat dissipation and LED lamps heat dissipation. The former is mainly related to board ,and selection and technology of the circuit, which temporarily won’t be discussed here. This article mainly introduces Led lamp heat dissipation, because LED chip made into Led lamp thus heat generated by Led chip will finally emit out to air through the shell of lamps. LED chip thermal capacity is small, thereby a little heat accumulation will make chip junction temperature increase rapidly; so, if heat dissipation is not good, its lifespan will be quickly shortened when working in the condition of high temperature for long time. However, this heat need go through many procedures to be emitted out chip to the outside air. In particular, the heat produced in the LED chip, emits out from metal heat block, first through solder to the aluminum substrate PCB, then through the heat conduction glue to the aluminum heat sink. So actually, LED lamp heat dissipation include heat conduction and heat dissipation in two parts.

However, LED lamp shell heat dissipation will choose different method according to the power size and operation place. Now basically has the following several kinds of heat dissipation methods:

Aluminum heat dissipation fin: the most common way of heat dissipation, use aluminum heat dissipation fin as a part of the shell to increase the heat dissipation area.

Thermal conductive plastic case: thermal conductive material is added when injecting molding into the plastic shell, to improve plastic shell’s ability of heat conduction and heat dissipation.

Air fluid mechanics using the lamp shell shape to create convection air, this is the lowest cost of improving the ability of heat dissipation.

Fan lamp shell internal reinforced with long life and high efficiency fan, this method has advantages of low cost and good effect. Merely, replacing fan will be troublesome, and it is not suited to be used outdoor. This design is relatively rare.

Heat pipe makes use of heat pipe technology to transform heat from LED chip to shell heat dissipation fin. In the large-scale lamps such as streetlight , this is a common design.

Overall current LED luminous efficiency is lower, leading to high junction temperature arising thus reducing lifespan. As we see, heat dissipation is a key issue for reducing junction temperature and lengthening lifespan.

sourcechipglen