This study comprehensively investigated the impact of indoor carbon dioxide (CO2) concentration on sleep quality. Three experimental conditions (800, 1900, 3000 ppm) were created in chambers decorated as bedroom and other environmental parameters that may influence the sleep quality were under strict control. Sleep quality of 12 subjects (6 men and 6 women) was monitored for 54 consecutive days through sleep quality questionnaire and physiological measures. Both subjective and physiological results showed that sleep quality decreased significantly with the increase of CO2 concentration, and the comprehensive questionnaire score at 3000 ppm was only 80.8% of that at 800 ppm. A linear positive correlation was found between sleep onset latency (SOL) and CO2 concentration, while a linear negative correlation occurred between slow‐wave sleep (SWS) and CO2 concentration. In addition, in the same sleep environment, men had higher subjective questionnaire scores after wake‐up, longer SWS and shorter SOL, which lead to a better sleep quality compared with women, and there was a significant gender difference in sleep quality at 800 ppm (P < .05).
The biophilic hypothesis states that human beings have an innate connection to nature. Accordingly, previous studies have shown that natural interior design elements may influence the occupants’ cognitive performance. This study investigated the effect of wooden elements on the occupant preference and cognitive performance of 20 adults (10 females and 10 males). Participants reported increased attention and productivity in wooden rooms versus a nonwooden room and were more likely to choose one of several wooden rooms over a concrete room as their preferred work environment. Participants also performed better on neurobehavioral tests in the wooden versus nonwooden environment. Participants’ average completion times decreased on average by 16 seconds, 5 seconds, 6 seconds, 16 seconds, and 7 seconds, respectively, for tests of Visual Reaction, Continuous Operation, Stroop, Calculation, and Meaningless Picture Recognition tests in the wooden versus concrete environments. On all five tests, participants gave more correct answers in the three wooden settings than in the concrete one. These results support the biophilic hypothesis; incorporating wooden elements into interior design may improve both occupant satisfaction and cognitive performance.
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