The colours of light in indoor environments: Mixing daylight and electric light spectra to define a proper match

The paper presents a simplified method to evaluate the spectral distribution of the light reaching an observer’s eye in indoor environments, when daylight and electric light are integrated. The method considers both the direct component of light and that reflected by the environment, starting from the actual spectral power distribution of the sources and the spectral reflectance of the indoor surfaces. The spectral irradiances at the eye level for a simple office located in two European cities (Naples and Bialystok) were analyzed considering different mixing conditions of electric light and daylight. Then Correlated Color Temperature (CCT), distance of the chromatic point from the Planckian locus (Duv), Circadian Stimulus (CS) and Equivalent Melanopic Lux (EML) values were obtained, in order to evaluate the quality of light incident at the eye level.