Research On Color Mixing Of Multicolor LEDs Based On PWM

Light source can affect the secretion of melatonin and cortisol by ipRGCs which is the third photoreceptor, and then have a significant impact on the physiology and psychology of human being. Dynamical adjustment of the light environment according to the season, mood, and daylight can improve the comfort of light environment for human. Therefore, white LED with adjustable CCT(correlated color temperature) and high Ra(general color rendering index) has been widely used in the intelligent lighting. In order to achieve the adjustable light intensity and CCT, the dimming of multiple LED is needed. This thesis presents a functional relationship between chromaticity coordinate and the duty cycle based on the multicolor mixing equations and the characteristics of PWM(pulse width modulation) dimming, that luminous flux is proportional to the duty cycle, to provide the theoretical support for the realization of intelligent lighting. The main steps of this research are presented as follow.1?According to the characteristics of PWM and Grossmann color law, the quantitative calculation model, which among chromaticity coordinate, correlated color temperature and duty cycles, for two and three channels' PWM dimming is established.2?The quantitative calculation model for two channels' PWM dimming has been verified favorably by light mixing experiments with WW/CW?Y/CW LED module. The results show that this model can be applied to two-color LED dimming with the advantage of high precision; WW/CW LED module owns a relatively stable and excellent color rendering properties and light efficiency.3?The light mixing experiments with R\G\B?R\G\CW?WW\G\B LED module has been applied in the verification of quantitative calculation model for three channels' PWM dimming. The results show that: 1. the Ra of R/G/B LED module is less than 40 and the light efficiency(LES) is the lowest in the dimming process; 2. The replacement of blue and green LED in R/G/B module by cold white and warm white LED with plentiful spectra is conducive to improving the Ra of mixed light. 3. WW/G/B LED module owns the best dimming effect.4?In order to obtain a definite solution of four color mixed equations, a MATLAB program is applied in the multi-constraint optimization simulation of the luminous efficacy(LES) and Ra of the mixed-light, the results of which are further verified by the experiments. The results show that: 1. R/G/B/WW?R/G/B/NW?R/G/B/CW?R/G/B/Y LED modules can produce a wide range of CCT from 2703 K to 7692 K. 2. Under the highest Ra achievable, the LES of the LED modules are relatively low, while the Ra of R/G/B/WW and R/G/B/NW LED modules can achieve 95 in the dimming process. 3. Under the highest LES achievable, the color rendering performance of the LED modules is relatively poor, but R/G/B/WW LED modules, R/G/B/CW LED modules and R/G/B/NW LED modules get their maximum LES value in the low color temperature section, high color temperature section and middle color temperature section respectively. By reducing the color rendering index, the luminous efficiency is improved significantly. The color rendering index can be increased by reducing the luminous efficiency. By balancing these two factors, we can achieve a high quality white light with high LES and Ra which are over 90...