From the junction temperature to speculate that life seems to be very simple, just check the graph in Figure 1, you can know that life for the junction temperature of 95 degrees you can get the LED life of 20,000 hours. However, this method is used for indoor LED bathroom downlights have a certain amount of credibility, if applied to the outdoor LED lamps, especially high-power LED lights, where there are many uncertainties. The biggest problem is the radiator cooling efficiency of led high bay lights is reduced over time. This is due to the accumulation of dust, bird feces makes its cooling efficiency. Also very strong because the outdoor ultraviolet rays also cause reduced life of the LED. UV is mainly the aging of the epoxy resin package play a big role, if the use of silicone, can be improved. There are some bad effects of UV on the aging of the phosphors, but not very serious.
Two voltage temperature to remove, you can get the temperature coefficient, expressed in mV / oC. For ordinary silicon diode, the temperature coefficient of about -2mV/oC. LED bathroom downlights most are not made of silicon, so its temperature coefficient should another go determination. Fortunately, various LED manufacturers data sheets, most of its temperature coefficient.
However, this method is used to relatively compare the two radiator cooling effect is more effective. Obviously, the volt-ampere characteristic left the smaller radiator, the heat the better. In addition, the life prediction of indoor LED bathroom downlights still have a certain degree of accuracy.