Light-environment interactions and integrative lighting design: Connecting visual, non-visual and energy requirements in a case study experiment

Beyond vision, light influences human circadian rhythms and buildings' energy consumption. Design solutions are needed to satisfy visual and circadian requirements while minimizing lighting energy demands. By reflecting the incident radiation, inner surfaces influence spatial and spectral light distribution, affecting the energy needed to achieve task illuminance and light-induced circadian response. Here, the walls' spectral characteristics' impact on the overall luminous environment and power demands is analysed in a test room, combining seven walls' colours and three sources' correlated colour temperatures (CCTs). Hence, the luminaires are set to meet visual needs: eye level spectral irradiances are measured, and light-induced circadian responses are obtained regarding both circadian stimulus (CS) and melanopic equivalent daylight illuminance (mel-EDI). It is found that both parameters are higher for highly reflective walls or those most reflective in the short-wavelength interval, being insufficient for proper circadian stimulation according to current guidelines. For all colours, the highest mel-EDIs occur with 6000 K CCT and the lowest for 3000 K CCT. On the contrary, CSs are generally higher for 6000 K and lower for 4000 K. Second, the power demands necessary to meet circadian requirements are calculated. With warm sources, sufficient CS and mel-EDI values are achieved for similar eye-level illuminance, requiring similar light outputs and power demands regardless of the wall's colour. In all the other cases, the light outputs and the corresponding power demands to achieve mel-EDI = 136 lx are much lower than those to reach CS = 30%, while those to achieve mel-EDI = 250 lx are quite always the highest.