Estimation of internal junction temperature & thermal resistance of light-emitting diodes using external luminous flux measurements

Although critical to the lifetime of LED, the junction temperature of LED cannot be measured easily. From the general photo-electro-thermal theory for LED systems, new equations for estimating the internal junction temperature T_j and junction-case thermal resistance R_jc of LED from the luminous flux measurements, which can be obtained relatively easily, are presented and verified practically. These equations provide a valuable tool for checking T_j in LED system design without expensive equipment.