Comprehensive impact of pre-sleep thermal and light environment on sleep quality in winter

Both pre-sleep thermal and lighting environments influence sleep quality through psychological and physiological pathways, with interconnected mechanisms. Despite this interdependence, limited research has systematically examined their combined effects. To address this gap, a three-factor, three-level orthogonal experiment was conducted. The environmental factors investigated were pre-sleep temperature (19 °C, 22 °C, 25 °C), illuminance (50 lx, 200 lx, 500 lx), and correlated color temperature (CCT) (2700 K, 4500 K, 6500 K). Subjective evaluations and objective measurements (wrist-worn accelerometer) were combined to assess sleep quality. During the experiment, a total of 184 sleep records were collected from 15 subjects (9 males and 6 females). The collected data were analyzed using ANOVA and other methods. The results showed that among the three environmental factors, CCT predominantly influences sleep latency, while illuminance primarily governs both sleep duration and subjective sleep quality assessment. Temperature exhibits the most pronounced effect on sleep stages. Our findings further reveal that establishing a comfortable thermal and moderately satisfying lighting pre-sleep environment can reduce sleep latency, wakefulness, and light sleep, and increase REM sleep, deep sleep, and sleep duration. Crucially, the synergistic interaction of temperature, light, and CCT surpass single or dual factor effects on sleep. Notably, CCT's independent effect on sleep latency exceeds its interaction with either temperature or illuminance; the interaction between temperature and illuminance on sleep latency is significant, but their independent effects are small. Finally, this study indicates that a neutral (22 °C) or slightly warm (25 °C) temperature and low (50 lx) or moderate (200 lx) illuminance are suitable for pre-sleep, and the appropriate CCT should consider the impact of blue light. This research provides a theoretical basis for the creation of comfortable thermal and lighting environments for sleep.