Analysis of LEDs thermal properties

One of the challenges of designing LED lighting systems is to ensure proper thermal management. It is known that during nonradiative combination phenomena[1-3] heat is generated in the active region of the LED but due to the high thermal resistance between this region and air much of the heat is conducted to the substrate. The problem is not that heat is generated but that it is not removed as fast as it is produced. In order to find solutions to this issue it is important to know as many parameters of the materials used to produce an encapsulated LED. This paper proposes an equivalent diagram corresponding to the thermal transient state, taking into account as many parts as possible of a power LED assembly including resistance and thermal capacitance of the embedded protection diode and calculates some time constants which occur on the chip-to-air via lens path. There are many equivalent schemes for the transient regime but they do not take into account the path followed by heat from chip to lens and very few calculate thermal resistances and thermal time constants. Knowing the thermal parameters intervening in transient regime, and implicitly knowing the thermal time constant, contributes to knowledge of the dynamic behavior of the LED but also provides information about the structure of the thermal device and this in turn will lead to a solution to provide adequate thermal management of the LED-based lighting systems.