The reasons for the LED junction temperature：
A. Undesirable component electrode structure，windows substrate or structure materials and conductive silver glue etc, have a certain resistance, these resistances accumulate with each other, constitute the series connection resistance of LED component. When current flows through the P – N junction, also flows through the resistance, producing joule heat, lead to chip temprature or junction temprature rising.
B. Because of P – N junction not extremely perfect, the injection efficiency of components can’t reach 100%, when LED working, P area injects charge into N area, meanwhile N area also injects charge into P area, generally, the later kind of charge injection won’t produce the photoelectric effect, but consumed in the form of heat. Even if the useful parts injected charge, also won’t all become light, some of them combine with defects or impurities of junction area，finally become hot.
C. Practice proved that the light efficiency limit is the main reason for the LED junction temperature rise high. At present, the advanced material growth and device fabrication processes have been able to make the LED input electric energy converted to optical radiation, however, due to the LED chip material compared to the surrounding medium has much larger refractive index, cause the great part of the photons in inner of chip (> 90%) cannot be successfully overflow interface, however, occurs total reflection between chip and medium interface, through the multiple internal reflection finally absorbed by chip material or substrate, and in the form of lattice vibration become hot, prompt LED junction temperature rising.
D. Obviously, the heat dissipation ability of LED components is a key condition to determine junction temperature high or low. When heat dissipation capability is strong, the junction temperature will drop, on the contrary, when the heat dissipation capacity is poor, junction temperature will rise.