Research On Methods Of Junction Temperature Measurement And Lifetime Estimation Correction In Accelerated Aging Test For LED Lighting Products

LED lighting products are becoming the mainstream type of lamps in the lighting market with the characteristics of low energy consumption,long lifetime and light weight.The tradition method for LED lifetime test requires more than 6000 hours of the test process,which costs too much time and resources.So the research on accelerated aging test for LED becomes a hot issue in the industry.Junction temperature is an important parameter in accelerated aging test model which directly influences the result of lifetime estimation.The junction temperature is considered to be a fixed value in the past lifetime estimation model,but some research shows that the junction temperature changes as time in the aging process.In this thesis,the methods for junction temperature measurement and lifetime estimation correction in temperature accelerated aging test for LED lighting products are studied.The main contents include four aspects.1.The decay rates of different phosphors mixed in white LED lighting product during accelerated aging test are studied.It is proved,by the spectral decomposition of mixed phosphor in LED lighting products during accelerated aging test,and the extraction of spectral characteristics of different phosphors,it is proved that the decay rates of different phosphors are unrelated to the blend,and different phosphors have different decay rates.So the relationship between the junction temperature and W/B changes during the accelerated aging process.2.The off-line test method of junction temperature off-line test of LED lighting product during accelerated aging test is studied.An experimental platform is established and seven LED samples are tested in two-step temperature-accelerated aging test.By the measurement of W/B ratio under different junction temperatures at different points of time,the relationships between junction temperature and W/B are established,and then the junction temperatures at the points of time are achieved.It is shown that the junction temperature has a good linear relationship as W/B ratio.In the two-step aging processes,the junction temperatures of LED samples working at ambient temperature of 25? are from 61.6? to 63.3? at the beginning,and from 71.7? to 73.2? in the end,with the increment distribute from 9.5? to 11.4?.The luminous fluxes are corrected by the junction temperatures,and it is shown that the uncorrected lifetime estimations have deviations form-12.8% to-18.6%,and from-12.5% to-20.3% for 80? and 70? accelerated aging test,respectively.3.An on-line accelerated aging test system for LED lighting product is established.The system contains accelerated aging part and optical inspection part,with an optic passageway connected,the system can perform the temperature accelerated aging and the on-line optical test for LED lamps.The simulation and analysis of key components are carried on.It is demonstrated that the measurement error of luminous flux is ±0.33%,and that of W/B is ?0.5%.4.The on-line test method of junction temperature of LED lighting product is studied which uses the established on-line accelerated aging test system.Twelve LED samples are in the experiments of two-step temperature-accelerated aging test.By the measurement of W/B ratio under different junction temperatures at different points of time,the relationships between junction temperature and W/B are established,and then the junction temperatures at points of time are achieved.It is shown that the junction temperature has a good linear relationship with as W/B.The junction temperatures of LED samples working under 80? are from 98.5? to 104.2? at the beginning of the first step of aging,and are from 108.4? to 112.7? in the end of the aging.The increment of the junction temperature are in arrange from 8.5? to 11.3?.The junction temperatures of samples working under ambient temperature of 70? are from 93?.4 to 97.3? at the beginning of the second step of aging,and are from 97.6? to 101.9? in the end of the aging.The increment of the junction temperature are in a range from 3.2? to 6.5?.The luminous fluxes are corrected by the junction temperatures.It is shown that the uncorrected accelerated lifetime estimations have deviations form-12.1% to-17.5% and-8.3% to-12.8% for the 80? and 70? accelerated aging test,respectively.With the obtained accelerated lifetimes under the two ambient temperatures,the activation energy can be calculated by Arrhenius model,and the lifetime of the LED product working under normal ambient can be then obtained.It is shown that the uncorrected lifetime estimation has a deviation of-14.7%.