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
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.