The effect of melanopic illuminance of illuminated environment on visual comfort, alertness and cognitive performance during e-book reading

Since the discovery of the fifth photoreceptor intrinsically photosensitive retinal ganglion cells, the influence of spectral composition of lighting conditions on visual and non-visual effects has drawn widespread concerns. Nevertheless, most studies did not systematically control the lighting parameters, resulting in potential confounding effects. This study examined the influence of melanopic equivalent daylight illuminance (mel-EDI) under different correlated colour temperatures (CCTs) levels on visual comfort, alertness and cognitive performance during e-book reading. Utilizing a 14-channel LED lighting system, the light spectra were modulated for two mel-EDI levels (higher and lower) under two CCT levels of 4000 K (105.94 lx and 59.66 lx) and 6500 K (133.73 lx and 83.76 lx), respectively. Moreover, a combination of subjective and objective measurements was applied, including questionnaires, physiological signal, cognitive performance and reaction time. The results showed that the illuminated environment with higher mel-EDI appeared brighter and enhanced alertness. Under 4000 K, the illuminated environment with lower mel-EDI induced less physiological discomfort, but brought more preference of e-book under 6500 K. Furthermore, viewers were more susceptible to the impact of mel-EDI under 4000 K than under 6500 K, supported by stronger fatigue physiologically under 4000 K.