Effects of blue-enriched white light with same correlated colour temperature on visual fatigue

Visual fatigue has become a public health issue, while the relevant retinal mechanism and characteristics of blue light that induce visual fatigue have been rarely studied. In the retina, both short wavelength-sensitive (S) cones and melanopsin-containing intrinsically photoreceptive retinal ganglion cells (ipRGCs) are sensitive to blue light, and their responses are opposite in pupil mediation. Thus, effects of blue-enriched white light with different S-cone-opic Equivalent Daylight Illuminance (EDI) on visual fatigue was investigated, maintaining the same melanopic EDI to avoid interferences of melanopsin-containing ipRGCs. Two white illuminants (one with low S-cone-opic EDI, the other with high S-cone-opic EDI) were characterized based on α-opic EDI with the same correlated colour temperature and illuminance. Melanopic EDI was lower than S-cone-opic EDI of these two illuminants. Psychological, visual, physiological and cognitive performances were measured to investigate visual fatigue. Results showed that blue-enriched white light with high S-cone-opic EDI can induce visual fatigue. Participants felt more discomfort in their eyes under high S-cone-opic EDI along with the decline of tear film stability and changes of heart rhythm. Furthermore, the reaction time in a memory task increased significantly under high S-cone-opic EDI. The findings provide new insights into the optimization of indoor lighting environments for human health.