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In this paper, optical power of high-power white-light-emitting diode (LED) devices is evaluated and characterized. A theoretical model for optical power is proposed. The measurements reveal that optical power decreases exponentially with junction temperature and increases linearly with current. The model considers conjunct effect of current and junction temperature on emitted optical power. The proposed theoretical model of optical power will facilitate the optical and thermal performance evaluation of LED devices and will be helpful to device design. With the presented optical power model, heat power can be estimated, because they are complementary to each other. Then, junction temperature of LED device can be predicted with known heat power. In addition, the optical power model can be applied to eliminate chromaticity shift phenomenon of trichromatic-based white-LED devices, simply by monitoring junction temperature and injection current of each chip. Validity of the optical power model has been verified by experimental measurements on two types of commercial LED devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]