# Physiological Study of Visual and Non-Visual Effects of Light Exposure
## 3 Experiment on Visual and Non-Visual Effects of Light Exposure
### Results and Discussion
#### 3.2.4 Electrodermal Activity  
This study calculated the deviations in the SCL over 1200 s (0-1200 s in constant light) from the average for 30 s (120-150 s in constant light) and defined their mean as a representative value. Then, the Mann-Whitney U test was performed to compare the results. Data from five participants were excluded because the instrument was disconnected during the experiment. Figure 13 shows the results for comparison one. Although a significant difference (\(p\) = 0.49) was not observed, the SCL in the RV condition had a higher mean than that in the BV condition. For six of the nine participants with visual effects for both light colors, the mean for red light was larger than that for blue light. These results suggest the possibility of sympathetic dominance due to the visual effects of red light [2; 4; 5]. The perception of red light may contribute to arousal as well as brain activity. Figure 14 shows the results for comparison two. Although a significant difference (\(p\) = 0.26) was not observed, the SCL in the BNV condition had a higher mean than that in the RNV condition. For three of the four participants with non-visual effects from both light colors, the mean for blue light was higher than that for red light. This may suggest sympathetic dominance due to the non-visual effects of blue light [7; 12; 13], implying that the large short-wavelength component of blue light may contribute to arousal as well as brain activity. Figure 12: Comparison of LF/HF ratio between RNV and RV. Figure 13: Comparison of SCL between BV and RV. Figure 15 shows the results for comparison three. Although a significant difference (\(p=0.59\)) was not observed, the SCL in the BNV condition had a higher mean than that in the BV condition. This implies the possibility of sympathetic dominance due to the non-visual effects of blue light [7, 12, 13], suggesting that the large short-wavelength component of blue light may contribute to arousal. Furthermore, the perception of blue light may contribute to sedation. Figure 16 shows the results for comparison four. Although a significant difference (\(p=0.23\)) was not observed, the SCL in the RV condition had a higher mean than that in the RNV condition. This may imply sympathetic dominance due to the visual effects of red light [2, 4, 5], suggesting that the perception of red light may contribute to arousal. None of the comparisons in this study demonstrated significant differences. A previous study reported that SCL did not differ significantly with different illuminance levels [48]. Therefore, the changes in light color may not have caused significant differences. Additionally, the previous study showed slight tendencies in the mean comparisons [49]. Although  
Figure 16: Comparison of SCL between RNV and RV. Figure 14: Comparison of SCL between BNV and RNV. Figure 15: Comparison of SCL between BNV and BV. no significant differences were confirmed in this study, all conditions showed tendencies in the mean comparisons, which were likely due to the effects of light color on EDA. The following presents the limitations of this study and future issues:
* This study set the red and blue light spectra to confirm the non-visual effects (i.e., the differences in the short-wavelength components of blue and red, especially from 446 nm to 477 nm). Simultaneously, to create an environment in which light color was not easily perceived, the long-wavelength component of red light was suppressed. Therefore, the red light used in this study may have been insufficient to induce visual effects;
* The participants were compared by grouping according to the presence or absence of visual effects based on their perceptual results. However, it is possible that individual differences, such as personal preference [2] for light color and light history (experience) [50], may have affected the comparison results.