Proposal of new thermal resistance for light-emitting diodes

In order to estimate exact thermal resistance of light-emitting diodes (LED), we introduced a new concept of effective internal optical power (IOP) of LED packages. It is because all photons generated at active region of LED chip cannot emit outside due to the difference of refractive index between a LED chip and an encapsulant material. The meaning of the effective IOP of LED package is non-thermal power of total power in LEDs. We derived a model for effective IOP and proposed a new thermal resistance using the effective IOP. To investigate pure thermal effect and distinguish optical effect in the LED packages, we carried out a computational fluidic dynamics simulations.