Contributions of melanopsin and illuminance of metameric white light on spatial brightness and pupil size

This study investigates the impact of melanopsin and illuminance on the pupillary light reflex and spatial brightness perception using metameric white light stimuli. A psychophysical experiment using the silent-substitution method was conducted at three typical indoor illuminance levels and two melanopic equivalent daylight illuminance (mEDI) levels. Results indicate that spatial brightness perception increases significantly with higher illuminance, while pupil size decreases with increased mEDI. Illuminance was identified as a secondary factor influencing pupillary reflexes, whereas mEDI played a secondary role in brightness perception. Doubling mEDI at constant corneal illuminance levels did not yield significant changes in brightness perception, indicating that brighter lighting strategies based on increased melanopic excitation should be implemented cautiously in practical settings. Additionally, the findings suggest that correlated color temperature (CCT) is not a reliable indicator of brightness perception.