Junction temperature of LED device used as an important parameter in its application is the core element of reliability measurement, but also the mainly research object of LED detection products. Here, this paper summarized the current reported on several LED junction temperature measurements, and made its application characteristics and limitations into comparison, made some improvements on forward voltage measurement on LED junction temperature technology program combined with the LED thermal stability of our company’s lighting test method.
In the mid 1990s, 20 century, Nakamura and others of Japan’s Nichia Chemistry Company made unremitting efforts to break through the blue LED creation key technologies. The emergence of GaN-based blue LED greatly expanded LED （ LED Tester ） applications, then opened the third generation semiconductor material GaN-based semiconductor lighting revolution. At the turn of the century, the world’s developed countries introduced national semiconductor lighting project plans to occupy the new top of semiconductor in the new century.
Nowadays,Chinahas taken the forefront in the world in LED lighting applications. According to the incomplete statistics, in 2009, Chinese lighting market had reached 28 million street lights, new and replacement street lights each year up to 3-4 million, created a hugeLED streetlights market. It was predicted that LED ( LED Testing System ) street lights of 2009 increased 178% than 2008, and the amounts will reach more than 8 million in 2011, penetration rate will reach 8.5%. Currently, during the promotion of LED applications, our country makes a strong support at the national level, the 2008 Beijing Olympic Games, the 2010 Shanghai World Expo and the current promotion of “Ten cities ten thousands plan” government demonstration projects by science and technology department and the China phased out incandescent light; speeded up the promotion of energy saving lamps (PILESLAMP) projects sponsored by National Development. Revolution Commission(NDRC)/United Nations Development Programme （UNDP）/Global Environment Fund(GEF) are all marked a breakthrough beginning of our country ‘s large-scale use LED ( LED Test Instruments ) energy saving lighting groups, has a great significance. Power LED is the key device during the development into the solid lighting. Although LED lighting has many advantages, to get the real meaning of the third generation lighting program, there still exists bottlenecks on measurements and applications, the LED device cooling and reliability issues, especially the gain issues of junction temperature state after formation of LED lighting groups.
As the current high power LED lighting are all assembled with more than one single tube LED lamps – multi chip LED, if cooling system design were unfitted, LED chip junction temperature would be too high, which would directly affect the LED device performance, resulting in low luminous efficiency, shortening the life expectancy, but also will make the LED photometric, colorimetric performance deteriorated.