Abstract
The rapid development of high efficacy and high-brightness light emitting diodes (LED) in recent years has made LEDs a very promising light source in the future. Among general approaches using LED to achieve white light, the multi-chip LED module approach provides a unique feature of color variability, i.e. control the color characteristics of a light source by changing the drive current. In a multi-chip LED module, each chip has a different spectral property, to control the module dynamically, it is necessary to incorporate a color sensor into the module. However, it adds the complexity to the driving and control circuits, as well as the cost and reduces design flexibility. In this work, we propose a method for predicting the performance of a multi-chip LED module under various operating conditions. The method essentially includes two parts: firstly, it employs an emission spectrum model which depends upon driving current and junction temperature, and, secondly, it applies a compact model to determine the junction temperature of each individual chip. Using this method, we have demonstrated the feasibility of determining the spectrum distribution of the multi-chip LED module using red, green, blue and amber colors. We have further demonstrated experimentally in this work, the color difference between the measured spectra and the modeling result can be controlled within 0.01 or less. This result satisfied the recommended deviation limit dictated by the lighting industry. Therefore, the performance of multi-chip LED module can be controlled accurately by an external feedback system without requiring a costly color sensor. This way, it could reduce the cost of a multi-chip LED module used for general lighting application.