Comprehensive analysis of LED street light cooling problem

At present, many people put their main eyes on the lumens of LEDs, and pay less attention to the heat dissipation of LED lamps. In fact, the lumens of LEDs are rapidly increasing. The single-watt lumens for mass-produced LEDs in 2006 have reached 50 lumens, and this number is growing rapidly. The theoretical theory of heat transfer corresponding to it has matured, and the heat transfer methods we can use are also 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 operational relationship between luminous flux (lumen) and radiant flux (Watt): where Km = 683 lm/w, which is the scale of the luminous flux, which is the scale of the radiant flux. That is to say, the 1W radiant flux may produce 683 lm of luminous flux in the most ideal case (blackbody radiation). Therefore, even if the luminous efficacy of the LED reaches 200 lm/w, the entire energy cannot be converted 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-standing problem.

At present, the heat dissipation methods of LED street lamps mainly include: natural convection heat dissipation, installation of fan forced heat dissipation, heat pipe and loop heat pipe cooling. Adding a fan to force the heat dissipation system is complicated, the reliability is low, and the heat pipe and the loop heat pipe heat dissipation method are high in cost. The street lamp has the advantages of outdoor nighttime use, the heat dissipation surface is located on the side and the body shape is restricted, which is beneficial to the natural convection heat dissipation of the air. Therefore, the LED street lamp is recommended to select the natural convection heat dissipation method as much as possible.

Possible problems in thermal design are:

　 1. The area of the heat dissipating fins can be set freely.

2. The arrangement of the heat dissipating fins is unreasonable. The arrangement of the heat dissipating fins of the lamps does not take into account the use of the lamps, 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 pipe, loop heat pipe, heat transfer resin, etc., they have not realized that heat ultimately depends on the external surface area of the lamp. go.

4. Neglecting the balance of heat transfer. If the temperature distribution of the fins is severely uneven, it will cause some of the fins (lower temperature parts) to have no effect or limited effect.

Now LED street lamp cooling technology, generally using the heat-conducting plate method, is a 5mm thick copper plate, in fact, it is a uniform temperature plate, the heat source is warmed off; there are also installed heat sink to dissipate heat, but the weight is too large. The weight is very important in the streetlight system, because the streetlight is 9 meters high, and if the danger is too heavy, it will increase, especially in the case of typhoons and earthquakes. Perhaps, in the future, LEDs will enter the field of street lamps extensively, and the formation of modular heat dissipation will better solve the problem of heat dissipation of LED street lamps.

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