Dynamic Photoelectrothermal Theory for Light-Emitting Diode Systems

This paper presents a dynamic photoelectrothermal theory for light-emitting diode (LED) systems. In addition to photometric, electrical, and thermal aspects, this theory incorporates the time domain into the generalized equations. A dynamic model for a general LED system is developed for system analysis. This theory highlights the fact that the luminous output of an LED system will decrease with time from the initial operation to the steady state due to the rising temperature of the heat sink and the LED devices. The essential thermal time constants involved in the LED systems are explained. The time factor is critical in understanding how much the luminous output will decrease with time and is essential to the optimal designs of the LED systems that are operated continuously (e.g., general lighting) or momentarily (e.g., traffic lights). Experiments on several LED systems at different time frames have been conducted, and the practical measurements confirm the validity of this theory.