Fast estimation of LED´s accelerated lifetime by online test method

High power light emitting diodes (HPLEDs) based semiconductor solid-state lighting has been hailed as the new energy-saving lighting source that can replace the conventional lighting sources due to its high efficiency, long life, environmental protection and compact size. So far, there are a lot of different LED products on the market, including LED bulb, LED spot light, LED landscape lamp, etc. All these LED products need to take a series of parameters testing before pushed to the market, among which the lifetime is an important one. However, to measure LED product´s lifetime by conventional process costs a lot due to long test time. Thus elevated temperature accelerated reliability test is usually used to obtain the accelerated lifetime, which is essential for projecting the product´s life under rated conditions. Most of the present accelerated test methods can be identified as “offline” methods, which mean the processes need to be stopped now and then for data acquisition. This will produce problems like small sample data capacity and further, disability to reflect small changes of the product performance within short time. So it is difficult to accurately predict the LED product life since the error is significant. In this paper, we provided an “online” test method. The accelerated temperature and driving current were set to 125°C and 350mA, respectively. An optical cable was utilized to transmit the LED-emitted light from high test temperature to room temperature so that the optical property parameters can be measured and acquired synchronously without throwing the detection equipment into the risk of overheat. During the whole process, the LED module was lighted. The degradation details were very clear. After around 420 hours, the output power declines about nine percent. According to Arrhenius model, the projected medium life L50 is calculated to be 3912 hours with high accuracy r2=0.95, which is much better than tho- e offline results. Therefore, in terms of lifetime projection, the operated time of accelerated life test could be shortened effectively on the guarantee of precision by this online method.