Comprehensive analysis of LED street lamp heat dissipation issues

At present, many people focus on the number of LED lumens , but pay less attention to the heat dissipation of LED lamps. In fact, the number of LED lumens is increasing rapidly. In 2006, the number of lumens per watt of mass-produced LEDs reached 50 lumens, and this value is still growing rapidly. The corresponding heat transfer theory system has matured, and the heat transfer methods we can use are basically clear: conduction, convection, radiation and phase change heat transfer (such as heat pipes). Therefore, the measures we can take on heat transfer or heat dissipation are visible and limited.

According to the calculation relationship between luminous flux (lumens) and radiant flux (watts): Km = 683 lm/w is the scale of luminous flux and Km = 683 lm/w is the scale of radiant flux. That is to say, 1W of radiant flux may produce 683lm of luminous flux under the most ideal conditions (black body radiation). Therefore, even if the luminous efficiency of LED reaches 200lm/w, it cannot convert all energy into light energy output, and the rest is converted into heat energy. In the long run, the heat dissipation problem of LED lamps will be a long-term problem.

At present, the main heat dissipation methods of LED street lights are: natural convection heat dissipation, forced heat dissipation by adding fans, heat pipes and loop heat pipes, etc. The forced heat dissipation method of adding fans is complex and has low reliability, while the heat pipe and loop heat pipe heat dissipation methods are costly. Street lights have the advantages of outdoor night use, heat dissipation surface located on the side, and less restricted size, which are conducive to natural convection heat dissipation of air. Therefore, it is recommended to choose natural convection heat dissipation for LED street lights as much as possible.

Possible problems in heat dissipation design include:

1. The cooling fin area can be set arbitrarily.

2. The layout of the heat dissipation fins is unreasonable. The layout of the heat dissipation fins of the lamp does not take into account the usage of the lamp, which affects the effect of the fins.

3. Emphasis on heat conduction and neglect of convection heat dissipation. Although many manufacturers have considered various measures: heat pipes, loop heat pipes, adding thermal grease, etc., they do not realize that heat will eventually be dissipated by the surface area of ​​the lamp.

4. Ignore the balance of heat transfer. If the temperature distribution of the fins is seriously uneven, some of the fins (the parts with lower temperature) will not work or have very limited effect.

At present, the heat dissipation technology of LED street lamps generally uses a heat conducting plate, which is a 5mm thick copper plate, which is actually a temperature-averaging plate to evenly distribute the heat source; there are also heat sinks installed to dissipate heat, but they are too heavy. Weight is very important in the street lamp system, because the street lamp is 9 meters high, and if it is too heavy, the danger will increase, especially when encountering typhoons and earthquakes, accidents may occur. Perhaps, in the future, when LED is widely used in the field of street lamps, modular heat dissipation may be formed to better solve the problem of heat dissipation difficulties of LED street lamps.