A proposed lighting-design space: circadian effect versus visual illuminance

Light causes not only vision, but also non-visual effects such as regulating the circadian system. Although the effort to fully understand the mechanism of non-visual response is still ongoing, quantitative models have been proposed to evaluate light's circadian stimulus based on the characteristics of light incident on human eyes. With the light-emitting diode (LED) technology providing flexibility in spectral design, it is now possible to tune lighting's circadian and visual effects to suit the uses of different built environments. Therefore, it is important to develop a lighting-design approach that considers both visual and non-visual aspects, and understand what combinations are achievable for general illumination applications. In this work, we propose a lighting-design space that allows the exploration of combinations of circadian effect and brightness (visual lit appearance). To demonstrate the feasibility of this approach, we develop a color-mixing method for four-channel color-tunable LED light sources, and maximize the gamut of the proposed space. This gamut represents the possible design objectives that interior lighting designers can target. As an example of application, we demonstrate that our color-tunable LED solution can be used to dynamically simulate both circadian and visual properties of daylight. (C) 2017 Elsevier Ltd. All rights reserved.