Abstract
Color-adjustable light sources facilitate both mood lighting and daylight harvesting. A single duty cycle can be used by a bi-color LED to adjust the correlated color temperature (CCT) by associating it with the duty cycle of the pulse width modulation dimming signal of the cool and warm white LEDs. The one-to-one mapping relationship between the single duty cycle and the CCT is based on the color mixing theory of bi-color LEDs. A method to correlate the dimming signals for bi-color LEDs is presented. The influence of the time characteristics of the two basic signals on dimming and CCT adjustment is analyzed. The dimming system of bi-color LEDs is designed, and the method used to adjust the CCT with a single duty cycle is verified. The experiment showed that the CCT can be accurately adjusted by the proposed method.
Highlights
Previous studies have shown that lighting color temperature and illumination can change people's visual perception and emotion; they play an important role in the control of human endocrine system activity, physiological rhythm, and psychological cognition [1,2,3,4]
To create a near-exact visual sensation and energy-efficient lighting, an artificial light source with independently tunable correlated color temperature and illuminance should preferably be introduced in daylight harvesting schemes [7,8]
A smart light source is characterized by its ability to adjust both the correlated color temperature and illumination, which is convenient for application in different environments, and achieves the goal of implementing one multi-use lamp
Summary
Previous studies have shown that lighting color temperature and illumination can change people's visual perception and emotion; they play an important role in the control of human endocrine system activity, physiological rhythm, and psychological cognition [1,2,3,4]. To create a near-exact visual sensation and energy-efficient lighting, an artificial light source (visually matched LED lamp) with independently tunable correlated color temperature and illuminance should preferably be introduced in daylight harvesting schemes [7,8]. For RGB three-color [9,10,11,12] or RGBA four-color LEDs [13], the Grassmann color law is applied to adjust the ratio of the luminosity of different color LEDs to produce white light. These types of LED systems require three or more pulse-width-modulated (PWM) output channels, which make them difficult to practically realize.
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