Effects Of Variation Of The Color Characteristics Of Lighting Sources By The Environmental Context

Over recent years the importance of using daylight in indoor environments to achieve reductions of energy consumption was largely discussed, but the use of daylight is even more important because of its effects on human beings. Daylight has a more uniform spectral distribution than the artificial sources (especially discharge lamps) and consequently it allows a better color perception; moreover it changes during the day both in intensity and spectral power distribution (SPD). For all these reasons, daylight ensures a high comfort in carrying out all the human activities and is also important to the circadian rhythm regulation; therefore it results necessary to evaluate the entrance of natural light in indoor environments both in qualitative and quantitative terms. Until now, the approach was mainly based on the daylight factor (DF) value, while the spectral composition of radiations coming from the sky was not considered. A proper use of daylight in indoor environments requires integration with electric lighting. Nowadays a designer can choose light sources with the most appropriate color tone, expressed by means of correlated color temperature (CCT); for indoor applications, the most popular are mainly fluorescent and LED sources, each disposable with different CCT. However, lit environments can be perceived differently under sources with the same CCT but different SPDs. In this paper, an analysis of the characteristics of daylight and electric lighting in an indoor environment is carried out, by comparing SPDs and CCTs of the natural source (sky) during typical winter days with contemporaneous measurements of spectral irradiances and CCTs detected at the eyes level. From results obtained, the influence of indoor environment over spectral distribution of radiations, both from daylight and electric light, was evaluated