LED Headlight heat dissipation

When it comes to LED bulbs, it is inevitable to talk about heat dissipation. As it is known to all, favourable heat dissipation effect can make sure the LED bulbs are bright enough and extend their service life. To reach a favorable heat dissipation effect in the limited space that LED bulbs live in, that means the maximum junction temperature of LED bulb should be lower than 80°C under the temperature of 50°C, which is a standard level.

Generally the power of car low beam and high beam would be between 40W to 60W, and it would be 80W and even higher of high-end automobile. What’s more, LED chip can change electricity into light, but only 30% of energy can make it and the other 70% turns into heat. Meanwhile, width lamp and turn light work together with them. With heat emitting from all these lights, it is difficult to lower the junction temperature. High junction temperature must bring about short service life. The following picture is about the relationship between junction temperature and service life.

Heat dissipation has a lot to do with space. That means in larger space, the cost of heat dissipation is lower. For example, as long as largen the cooling aluminum base of street lamp, the problem of high junction temperature can be solved. If the space is limited, however, artificial graphite cooling fin is employed to disperse energy and equalize the temperature of heat source surroundings, which is more expensive. So, the first discussion is about  encapsulating material.

Most LED headlights uses CPS packaging technique and it contributes to heat dissipation from three aspects. Firstly, how much heat produced from its wattage. Secondly, heat conductivity of the material affects the average temperature. Thirdly, how wide is the material. The following pictures will let you know what kind of material is best for heat dissipation.

Although the LED headlight is large enough, its space for cooling is not that large. Additionally, more and more car manufacturers use high-power LEDs as many as possible. The front of light is for LEDs and reflector and the rear is for heat dissipation appliance. How to reach temperature equalization and conduct junction temperature with shortest time? The encapsulating material plays an important role in solving this problem.

The following pictures show the thermal structure analysis under various driving current. Take pic 4 as an example, ceramics fluorescent fin is only 2.5°C lower than glass when it comes to 150mA electric current while the temperature difference is up to 20°C when the electric current is up to 800mA.

When drive current is 150mA,

When drive current is 800mA,

When analyzing the material of encapsulated structure, I found that chip and fluorescent material contribute most to heat dissipation. Replacing chip and fluorescent material with better material is ideal but it cost a lot. To be economical and effective, changing fluorescent material is a better choice.

One more thing, heat source transfers radiation to the surface of heat conductor and after that it let out to the air. If gas convection is relatively slow and passive, it will raise the difficulty to heat dissipation. One of the effective ways to cool down is to add a cooling fan and heat pipe. Well, it is harder than it sounds. Every addition of a component will raise possibility to invalidation, not to mention the cost. Therefore, heat dissipation technique and appliance result in the fact that LED headlights have great price gap on the market.