| dc.description.abstract | Because of the rapid development in solid-state light technology, the luminescence efficiency of LEDs has been grown up from 50 lm/W in 2009 to 250 lm/W in 2008. LEDs have an extreme potential for future lighting. Besides, combining with the second optics component designed by the light distribution of LEDs, there are all kinds of LEDs products, such as car headlamp, light module for medical treatment, streetlight, and bike lamp etc. However, light emission properties of LEDs, for example light power and chromaticity, would be changed as the operation time goes by. The major factor caused this phenomenon is heat arisen from LEDs under electric current driving. Thus, how to effectively evaluate and manage the thermal effect to achieve an expected luminescence efficiency, is one of most important topics in LED lighting technology.
In this dissertation, an accurate model for LEDs’ emission spectra dependent on electric driving current and junction temperature is developed. Based on this emission-spectra model, light-emission characteristics of LEDs could be clearly described under different electric driving conditions, such as light power, light chromaticity and color temperature. And, in this dissertation, an effective method for stabilization on emission spectra of LEDs is proposed. Under this controlled method, light-emission characteristics could be stabilized on a steady state, and are independent on the thermal effect.
First we propose a model for precisely describing the emission-spectra distributions of various colored LED through an aid of the experimental data measured by an integrating sphere system. In addition, we developed a system for measuring the junction temperature of LEDs and made this junction temperature to be an influenced factor in this emission-spectra model. Thus, this emission-spectra model could be utilized to predict LED’s emission spectra under different electric driving current and junction temperature, and fit in with the practical situations.
Furthermore, we develop a controlled method for stabilization LEDs’ emission spectra. This method is implemented by an active-controlled heat sink and a proper electric current. As results shown, this method could not only modulate, but also stabilize LEDs’ emission spectra. Thus, the light emission characteristics of LEDs could be modulated and stabilized under this method, including light power and light chromaticity of LEDs.
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