Thermal Analysis And Design Of High Power Led Street Lamps

LED (Light Emitting Diode) is a kind of solid-state lighting source which transforms electricity into light directly. It is a new lighting source which has the advantages of long lifetime, low energy consumption and environmental protection comparing with other light sources, so it has been used in some general lighting. Street lamp is one kind of typical general lighting applications. In order to meet the illumination requirement, LED street lamps should work in high power. For the high power LED street lamps, good light extraction is the most important thing, but about 80 percent input power is transformed into heat, if the heat can not be dissipated efficiently and rapidly, the temperature of LED junction will be going up, actually, there have been many reports about early failures of street lamps, called dead lamps which have been regarded as a barrier in the public and administration acceptance of LED street lamps, so thermal management is very important for high power LED street lamps.This paper introduced the whole process from the principle of LED lighting to the materials of LED street lamps firstly and then focused the eyes on the heat dissipation of the typical high power LED street lamps.A multi-chip thermal resistance network model was applied to estimate the temperature distribution of LED street lamp. Experiment was firstly done to obtain temperatures of several locations in a prototype LED street lamp. Then the multi-chip thermal spreading resistance model was established to calculate the full temperature distribution. Comparison between the model calculation and experimental measurement showed a good agreement, which demonstrates that the present model can be used in engineering design to estimate the temperature distribution of high power LED street lamps. From the multi-chip thermal resistance network model, it is found that the thermal spreading resistance and the convection heat transfer resistance have a crucial impact for the heat transfer.In order to decrease the thermal spreading resistance, a vapor chamber base structure was put forward in the paper. It works between small size heat source and large size heat sink, a kind of low boiling temperature liquid changes to vapor by the absorption of heat from the heat source and the vapor condenses into liquid by releasing heat to the heat sink, then the liquid is back to the heat source well-proportionally and then begins a new cycle. Experiment was done to verify the accuracy of the idea, results show that heat could be exchanged symmetrically in a short time and the vapor chamber base structure is available to decrease the spreading resistance. In order to decrease the convection heat transfer resistance, design and optimization method of plate fin heat sink based on the minimum resistance was presented to improve the heat dissipation efficiently between the heat sink and the ambient. To prove the feasibility of the present design and optimization method, an 112W LED street lamp was manufactured and experimentally investigated based on the design. The experimental result was that the average heat sink temperature remained to be stable at 44℃when the ambient temperature was 25℃, the average temperature difference between steady heat sink temperature and environment temperature was 19℃and this temperature was design to be 18℃. Comparing the results achieved by the design with the ones by the experiment, it is found that the design and optimization method is feasible and works well for the heat sink design of the high power LED street lamp.At the end of the paper, the idea of four-in-one packaging structure was proposed which puts the chip, optical design, electronic design and heat dissipation into one packaging module.