aims at meeting human vision and health requirements. Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) appear to play an essential role in stimulation of the non-image forming effects and thus human health and well-being. There are indications that radiation incident contributes to the magnitude of these effects. This review summarizes current studies on humans and animals related to radiation directionality as well as the spatial distribution of ipRGCs on the retina. New insights can facilitate and optimize the incorporation of radiation directionality in building lighting design.