(Hangzhou Zheda Tricolor Instrument Co., Ltd.      Hangzhou 310013 ) Abstract: The thermal performance parameters of LED mainly refer to junction temperature and thermal resistance. The thermal performance parameters have significant influence on the photoelectric color parameters of LED . This paper introduces the important influence of LED thermal performance on its output characteristics by measuring the typical LED . The significance of the measurement method. The principle of illumination of LEDs is in the forbidden band of semiconductors, the combination of electron and hole pairs. However , of the electrical energy injected into the LED device, only about 15% of the electrons and holes recombine with radiation, emitting photons, and about 85% of the electrical energy is converted into heat. The thermal performance of LEDs directly affects their luminous efficiency, wavelength, forward voltage drop, reverse breakdown current, and device lifetime. Traditional Φ3mm and Φ5mm LED devices due to the drive current, less heat, thermal impact was not significant in recent years, with the rapid development of power LED devices, LED thermal properties affect more and more obvious, by the people's attention . Second, LED thermal performance       The thermal performance parameters of LEDs mainly refer to junction temperature and thermal resistance. The junction temperature of the LED refers to the temperature of the PN junction. The thermal resistance of the LED generally refers to the thermal resistance between the PN junction and the surface of the housing. The junction temperature is a parameter that directly affects the operating characteristics of the LED , and the thermal resistance is a parameter indicating the heat dissipation performance of the LED . As shown in Figure 1 , T j is the junction temperature, T a is the ambient temperature, T b is the temperature of the stent , R thba is the thermal resistance from the point of the stent to the environment, and R thjb is the PN junction to the point of the stent. Thermal resistance, R thja is the thermal resistance between the PN junction and the environment. Figure 1 : LED junction temperature and thermal resistance Third, different conditions of the LED       The junction temperature is affected by the ambient temperature and operating current. Thus, changing the LED current and the ambient temperature may affect the analysis of the thermal performance of the LED of the LED.       Using the standard LED test system, the influence of current and ambient temperature on the operating characteristics of the LED can be analyzed . Taking a power white LED as an example, the rated operating current of the sample to be tested is 350 mA .
Keywords: LED  temperature  measuring 