*4.4. Research Limitations*

In addition to the exaggerated color temperature differences between the overcast and clear skies, this study contains the following limitations. First, the participants in the studies are experts in architecture designs. Assessments of non-experts were not included in this study. Second, this study only measured the EEG on the left and right prefrontal lobe areas, other channels require further exploration. Third, this study only included 41 participants' valid responses. More participants with diverse distributions of age ranges could provide more concrete conclusions.

#### **5. Conclusions**

This paper presents a laboratory experiment using VR scenes. Nine aperture designs, two window sizes and two sky types were explored. Forty-one participants with four years or longer architecture background evaluated eight aspects of interior natural lightscape. Physiological data of both ECG and EEG of the prefrontal lobe areas were collected during the experiment. According to the data analysis, the aperture designs have impacts on subjective assessments of calmness, interest, excitement, complexity, spaciousness and satisfaction with exterior views. The sky types influence subjective assessments of pleasantness, calmness, interest, excitement, complexity, spaciousness, brightness and satisfaction with exterior views. Compared to the small window, the large window enhances beta oscillations and beta power on the right prefrontal lobe area. Compared to the overcast sky, the clear sky attenuates the theta rhythm on the prefrontal lobe areas.

Based on the subjective responses, the design recommendations are proposed as below:


4 Finally, openness ratios of aperture designs, which had great a impact on subjective impressions of spatial spaciousness and satisfaction with exterior view amounts, need be considered during the aperture and façade design.

**Author Contributions:** Conceptualization, Z.K., K.H. and C.L.; methodology, Z.K., K.H. and C.L.; software, Z.W. and F.C.; validation, Z.K., K.H. and C.L.; formal analysis, Z.W., F.C., Y.L. and X.L.; investigation, Z.W. and F.C.; resources, Z.K., K.H. and C.L.; data curation, Z.K.; writing—original draft preparation, Z.K. and K.H.; writing—review and editing, Z.K., K.H. and C.L.; visualization, Z.K., Y.L. and X.L.; supervision, C.L.; project administration, Z.K.; funding acquisition, K.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by National Natural Science Foundation of China (Grant No. 52208012), Natural Science Foundation of China Youth Science Foundation (Grant No. 51908301), National Natural Science Foundation of China Youth Science Foundation (Grant No. 51908111), General project of Shandong social science planning and research project (Grant No. 21CSHJ06), Shandong Natural Science Foundation Training Fund (Grant No. ZR2019PEE034) and Qingdao social science planning and research project (Grant No. QDSKL2101178).

**Acknowledgments:** The authors would like to thank these six students for their help with data collection: Ruyan Zhang, Xingqi Kong, Pengxuan Ning, Jinghao Ni, Jiayue Wang and Qilin Liu. The authors also would like to thank the 44 participants, who contributed their time, enthusiasm and valuable feedback to this experiment.

**Conflicts of Interest:** The authors declare no conflict of interest.
