Non-visual effects of office light environment: Field evaluation, model comparison, and spectral analysis

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Light environment is an important part of the office environment. Aside from visual effects, light also has non-visual effects, for example, on mood, alertness, and performance. Although essential for healthy light design, current office lighting rarely considers non-visual effects. The evaluation of non-visual light environment is predominantly based on two physiological models: the equivalent melanopic lux (EML) and circadian stimulus (CS) models. EML is similar to visual illuminance but the spectral sensitivity function is non-visually converted. CS indicates the percentage of melatonin suppression and is more complex as it considers the interaction between different photoreceptors. Model comparison and spectral analysis of field measurements are required to verify the applicability of these models. Therefore, this study conducted field evaluations of non-visual effects in several typical office environments with different window orientations, then compared the calculation differences between EML and CS models. Errors in the spectral approximation calculations were also analyzed. According to the analysis of 571 measured data sets, no workstation with existing layout met the non-visual standards under overcast conditions. EML and CS models are similar in office indoor environment compliance evaluation, but CS model gets more reasonable results at high eye-level illuminance. Moreover, daylight irradiances were effectively approximated by the CIE standard illuminants D50 and D55. The conclusions of this study can be used as guidelines for interior design, field evaluations, and daylight simulations of the non-visual effects of light in office environments.