A Study on the Non-Visual Optical Characteristics of Indoor Lighting Products According to Luminous Flux and Correlated Color Temperature

This study investigates the impact of illuminance and correlated color temperature (CCT) on melanopic responses mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) to characterize the non-visual optical properties of indoor lighting. Eleven commercial fixtures-four human centric lighting (HCL) products and seven smart lighting devices—were measured in a darkroom using CIE S 026 metrics, including melanopic efficacy of luminous radiation (MELR), melanopic daylight efficacy ratio (MDER), melanopic equivalent daylight illuminance (MEDI), and M/P ratio. Results showed that MELR, MDER, and M/P ratio increased proportionally with CCT but were largely unaffected by illuminance. Conversely, MEDI increased with illuminance rather than CCT. No significant differences were observed between HCL and general smart lighting products under equivalent CCT and illuminance conditions. These findings highlight the importance of spectral power distribution, particularly in the 480–490 nm range, for optimizing circadian effects and suggest the need for further research using larger datasets and additional circadian metrics, such as circadian stimulus (CS) and circadian light (CLA), to support standardized evaluation and design of non-visual lighting performance.