1, What is the LED junction temperature?

LED's basic structure is a semiconductor of the P-N junction. Experiments that when current flows through the LED element, when, P-N junction temperature will rise, strictly speaking, put the P-N junction area is defined as the temperature of LED junction temperature. As the components are usually all have a very small chip size, so we may also be regarded as the temperature of LED chip junction temperature.

2, resulting in LED junction temperature of the reasons for what?

In the LED work, the following five conditions can exist in varying degrees to promote the junction temperature rise:
a, negative electrode components, structure, window layer of substrate material or the junction area, as well as silver conductive adhesive Dengjun There is a certain resistance value, which increases resistance of each base to form LED component series resistance. When the current flows through the P-N junction at the same time will be flowing through these resistors, resulting in Joule heat, resulting in chip temperature or junction temperature rise.
b, due to the extreme P-N junction can not be perfect, components, injection efficiency is not 100%, which means that in addition to P zone LED work area to the N into the charge (hole) outside, N districts will also to the P District, injected charge (electrons), under normal circumstances, the latter category is the charge injection will not produce the photoelectric effect, but in the form of heat consumed. Even if the useful part of the injected charge, it will not all become the light, some of the junction area with the combination of impurities or defects, will eventually become heat.
c, proved a light efficiency of LED junction temperature limit is increased leading to the main reason. At present, the growth of advanced materials and components, LED manufacturing process, has enabled the vast majority of input energy converted into light radiation, but because the LED chip material, compared with the surrounding medium, has a much larger refractive index, resulting in chip internally generated very most of the photon ( "90%) can not be successfully overflow interface, media interface in the chip and produce total reflection, to return chip and through a number of internal reflections were eventually absorbed silicon material or substrate and to lattice vibrations form into a hot, prompting junction temperature rise.
d, obviously, LED components, the heat dissipation capability is to determine the junction temperature is another key condition for high and low. Cooling capability, the junction temperature decreased, conversely, when the junction temperature of poor heat dissipation will increase. As the epoxy adhesive is a low thermal conductivity material, so the P-N junction at the heat generated is difficult to circulate upward through a transparent epoxy into the environment, most of the heat through the substrate, silver paste, shell, epoxy adhesive layer, PCB with heat sink downward divergence. Clearly, the related materials will directly affect the ability to conduct heat dissipation efficiency of the thermal component. A common type of LED, from the P-N junction area to the ambient temperature the total thermal resistance of 300 to 600 ℃ / w between the well-structured for a power-type LED components, the total thermal resistance of about 15 to 30 ℃ / w. A huge difference in thermal resistance, shows that common type of LED components, only a very small input power conditions, in order to work properly, while the power dissipation of power-type components can be as large as watts or even higher.