Abstract: The aim of the present study was to investigate the effect of indoor Illuminance on healthy adults’ cognitive performance, subjective mood and alertness during daytime office hours. In addition, this study also examined whether the relationship between daytime light exposure and cognitive performance is mediated by subjective mood and alertness in healthy adults. A single factor between-subject design with Illuminance at eye level (300 lx vs 1200 lx) as the independent variable was employed in the current study. A total of 106 participants took part in the formal experiment according to some strict selection criteria, such as chronotype, medical and sleep disorders, general health, life habits, affective disorders, smoking, drug consumption, body mass index, shift work and transmeridian flights during last 2 months. Based on previous findings, the present study hypothesized that exposure to bright light would promote task performance compared to the dim light, and bright light would have a beneficial effect on positive mood and subjective alertness. In addition, it was also hypothesized that subjective alertness mediates the relationship between bright light exposure and three indicators of cognitive performance: working memory, long-term memory and inhibitory capacity; positive mood mediates the relationship between bright light exposure and three indicators of cognitive performance of working memory, long-term memory and inhibitory capacity. Results showed that participants responded faster on Go/No go and 2-Back task under bright light exposure compared to the dim light exposure, while there was no significant difference on accuracy of these two tasks; in contrast, no significant effect of indoor Illuminance on Long-term memory task was observed in the current research. Subjective alertness and positive mood were also significantly improved in the high illuminance (1200 lx) in comparison with the low illuminance condition(200 lx). Correlation analyses among Illuminance levels, positive mood, negative mood, subjective alertness and task performance (Go/No go, 2-Back) revealed that there were positive correlations between Illuminace level and positive mood, subjective alertness and Go/No go task; negative correlations between Illuminance level and subjective alertness, Illuminance level and Go/No go task, Illuminance level and 2-Back task, positive mood and subjective alertness. The multivariate stepwise regression analysis indicated that Illuminance and subjective alertness were significant factors in predicting Go/No go performance, and also Illuminance and positive mood were significant factors in predicting subjective alertness. Based on correlation and multivariate stepwise regression analysis, a relational model was established and results showed that the effect of indoor Illuminance during daytime on Go/No go task was fully mediated by subjective alertness, and the relationship between Illuminance and subjective alertness was partially mediated by positive mood. It should be noted, however, that no mediating effect for negative mood was found in both the relationships between Illuminance and cognitive tasks, the subjective alertness and indoor Illuminance. These findings suggest that even during daytime office hours, bright light exposure did have a beneficial effect on task performance, positive mood and subjective alertness. Additionally, subjective alertness was a key variable in the effect of indoor Illuminance during daytime on cognitive functions, especially for the attention-related performance.

Key words: Illuminance, Cognitive performance, Subjective mood, Alertness, Mediating role, Daytime

摘要： 本研究采用单因素被试间设计，考察了白天室内照度(300 lx vs 1200 lx, 眼位位置)对认知加工的 影响及主观情绪和警觉性在照度水平与认知加工间的中介效应。结果发现：(1)被试在高照度照明条件下的 认知加工绩效(Go/No go, 2-Back)明显好于低照度照明；(2)室内照度对积极情绪和主观警觉性具有显著的正 向影响；(3)警觉性在照度水平对Go/No go 任务的影响中起着完全中介作用，情绪的中介作用不显著。 这表明警觉性在室内照度与部分认知加工间扮演着重要的“桥梁”作用。

关键词: 照度水平, 认知加工, 主观情绪, 警觉性, 中介效应, 日间