Research On Liquid Cooling LED Indoor Lamp

About70percent to80percent energy is converted to heat when LED works. Itcauses high junction temperature and bad performance. The thermal problem becomesmore serious when the power increases. Therefore, it is of great value to solve thethermal problem of LED lamp. Metal heat sink is the main cooling method for indoorLED lamp which power is no more than10W. However, metal heat sink increases thecost of LED lamp and this lamp is more expensive than the traditional lamp and it isdifficult to accept for the users. In addition, the thermal conductive silicon layerbetween MCPCB and heat sink can hardly dissipate heat effectively and it will easilycause higher PN temperature. To solve these problems, a liquid cooling method isproposed. Heat dissipation performance of this kind lamp may be better and its pricewill be lower. However, there is little work has been done but ads and patents of thislamp. In this paper, the thermal performance will be researched from the theory,experiment and simulation aspects and it will provide reliable basis for the productpromotion.①Based on the heat transform theory, the structures of the metal cooling andliquid cooling LED lamps are analysised, the thermal resistance models of the twolamps are built, the feasibility of the liquid cooling is proved.②Constant temperature heating system is built, the transmittance of the liquidand the spectrum before and after test is measured, the suitable liquid and light sourcesare choosed. It is found that the transmittance of transformer oil after test decaysseriously, the transmittance of silicone oil has no significant change and the valuesbefore and after test are all above0.9, the spectrum distribution of LEDs after test haveno obvious change.③On the basis of junction temperature measurement by forward voltagetemperature method, the test system is built. The voltage-temperature coefficients ofLEDs are calibrated, the junction temperature of the lamps at different current ismeasured and the stable temperature fields are simulated. It is found that The junctiontemperature, the MCPCB temperature and the shell temperature of the liquid coolingLED lamp are lower than those of metal cooling lamp. The error between simulatingvalues and experimental values is less than6.4%.④The single factor influence of the liquid cooling structure on the heat dissipation performance is studied, the main influence factors are obtained. Thestructure is optimized by orthogonal method. It is found that the diameter of shell, theliquid level and the diameter of MCPCB are the main influence factors, and the finaloptimization result is45mm,30mm and16mm. It is also found that junctiontemperature linear changes with power and the liquid direct cooling way applies to heatdissipation of indoor lamp which power is within10W.⑤The lifetime experiment system is built, the luminous attenuation at differentcurrent is measured and the lifetime of lamp is estimated. It is found that the lifetime ismore than25000h when the current is less than700mA, and the lifetime is about6000hwhen the current is about900mA but it can meet the lighting requirement. Compare theperformance and price of the two lamps, it is found that the liquid cooling mathod canreduce the cost of lamp and improve the luminous flux and finially improve theperformanceprice ratio.