Metrics of non-visual effects of light

The discovery of a new photoreceptor ipRGC (melanopsin) and the associated non-visual impact of the lighting environment on human well-being and health has led to a significant amount of research in the field of the connection between the parameters of light sources and human biological activity. The results of studying the non-visual effect of light are successfully applied in circadian lighting, which is based on changing the correlated colour temperature (CCT) of light sources of indoor lighting system during the day in accordance with the natural change of this parameter, and contribute to maintaining the biological processes of vigilance and preparation for sleep. However, the study of the light sources parameters for indoor lighting that can affect human well-being is not limited only to their CCT. After more detailed study of the radiation spectrum influence on the concentration and dynamics of melanopsin, the International Commission on Illumination (CIE) has proposed an algorithm for determining the melanopic irradiance and melanopic illuminance precisely by the spectral distribution of irradiation sources. To quantify the ratio of the non-visual impact of the lighting environment parameters on human well-being, the ratio of the melanopic flux M to the photopic luminous flux P for a test light source, which is a dimensionless quantity, can be used as a new ratio M/P. By definition, this ratio is normalized to 1 for the reference daylight illuminant D65. This ratio can be applied for creating a new lighting metric that can characterize LED light sources in terms of its potential for non-visual impact depending on its spectral characteristics. Moreover, new metrics of non-visual light impact will be helpful for the implementation of integrative lighting principles declared by the CIE as balance between human well-being, health, and functioning lighting for achieving the energy savings and reducing the impact on environment by applying LED systems with the considered characteristics.