The impact of melanopic illuminance on alertness assessed by electroencephalography and Karolinska Sleepiness Scale

Abstract

Light is considered to have a range of important non-visual effects on the human body, including its influence on alertness. However, it remains unclear which lighting factors directly influence alertness: although rising photopic illuminance has been reported to enhance alertness, it may not be the fundamental factor; the roles of photoreceptor-weighted spectral metrics, such as melanopic equivalent daylight illuminance (m-EDI) and cyanopic illuminance, remain to be further investigated. This study conducted a human-factor experiment involving 22 participants to investigate the effects of m-EDI and cyanopic illuminance on alertness, which was assessed using electroencephalography and Karolinska Sleepiness Scale (KSS). The results showed that as m-EDI increased, the ratio of β-wave energy to total brain wave energy significantly increased while KSS scores decreased, indicating an enhancement in alertness. On the other hand, no significant differences in alertness were observed with varying cyanopic illuminance levels based on both assessment methods. Additionally, regression analysis indicated that, compared to photopic illuminance, m-EDI was more accurate in predicting individual alertness. Furthermore, we investigated the quantitative relationship between m-EDI and alertness levels and observed that at higher m-EDI intensities, changes in alertness tended to reach saturation, with an m-EDI threshold around 260 lx. In conclusion, our study shows that m-EDI is a key lighting parameter that influences alertness.