Mr. Jiyong Wang Profile

Jiyong Wang

at Zhejiang Univ

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Proceedings Article | 15 October 2012 Paper

A quantitative dimming method for LED based on PWM

Jiyong Wang, Tongsheng Mou, Jianping Wang, Xiaoqing Tian

Proceedings Volume 8484, 84840D (2012) https://doi.org/10.1117/12.970576

KEYWORDS: Light emitting diodes, Light sources and illumination, LED lighting, Electrodynamics, Chromium, Light sources, Visualization, Modulation, Retina, Amplitude modulation

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Traditional light sources were required to provide stable and uniform illumination for a living or working environment considering performance of visual function of human being. The requirement was always reasonable until non-visual functions of the ganglion cells in the retina photosensitive layer were found. New generation of lighting technology, however, is emerging based on novel lighting materials such as LED and photobiological effects on human physiology and behavior. To realize dynamic lighting of LED whose intensity and color were adjustable to the need of photobiological effects, a quantitative dimming method based on Pulse Width Modulation (PWM) and light-mixing technology was presented. Beginning with two channels’ PWM, this paper demonstrated the determinacy and limitation of PWM dimming for realizing Expected Photometric and Colorimetric Quantities (EPCQ), in accordance with the analysis on geometrical, photometric, colorimetric and electrodynamic constraints. A quantitative model which mapped the EPCQ into duty cycles was finally established. The deduced model suggested that the determinacy was a unique individuality only for two channels’ and three channels’ PWM, but the limitation was an inevitable commonness for multiple channels’. To examine the model, a light-mixing experiment with two kinds of white LED simulated variations of illuminance and Correlation Color Temperature (CCT) from dawn to midday. Mean deviations between theoretical values and measured values were obtained, which were 15lx and 23K respectively. Result shows that this method can effectively realize the light spectrum which has a specific requirement of EPCQ, and provides a theoretical basis and a practical way for dynamic lighting of LED.

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