Comparison of Spectral Power Distribution of Various Light Sources in Correlation to Human Circadian System

Non-visual effect of light to human beings are still intensively researched in these days. This paper is focused on investigation of spectral power distribution (SPD) of various light sources in correlation to human circadian system. They were chosen light sources suitable for residential lighting including modern light emitting diodes (LED) with different correlated colour temperatures (CCT), which was normalized to same luminous flux value so that comparison would be reliable. It is known that non-visual photoreceptors via melanopsin photoreceptors (intrinsic photosensitive Retinal Ganglion Cells-ipRGCs), which are co-responsible for synchronization of circadian rhythm, requires blue spectral components in the light with a maximum spectral sensitivity around 460 – 480 nm, therefore this spectral region was studied in details.