Sleep is closely related to human physical and mental health.Insufficient sleep has been linked to adverse outcomes including obesity, cardiovascular diseases, diabetes, early-onset dementia, and Alzheimer's disease. 1,2 Sleep stages are divided into non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep, which alternate cyclically across a sleep episode. 3 NREM sleep can be further divided into three stages of N1, N2, and N3. 4 N1 stage and N2 stage are referred as light sleep while N3 stage is referred as deep sleep, and deep sleep is beneficial to energy recovery. Sleep quality could be affected by many factors. Sleep environment, involving temperature, lighting, and air quality, is one of prime factors affecting sleep. 5 Compared with other factors like psychology state and body condition, sleep environment can be easily adjustable and controlled, which is worth further investigating for explicit evidence. Many field researches reported that poor sleep environment, for example, polluted indoor air quality and

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