## 3 Results
### Analyzing Illuminance Levels to Which the Participants Were Exposed  
Figure 4 shows photographs of the fabricated circadian light meter. To analyze the illuminance to which participants were exposed, the circadian light meter was fixed to the visor of their hats through a fixture printed by a 3D printer. The weights of the fixture and the circadian light meter were 12 g and 17 g, respectively, and they were not bothersome to the participants while wearing the hat. Figure 5 shows the results of the intra-daily light exposure of the participants and sunlight measurements for the corresponding time, both obtained using the developed circadian light meter. Figure S7 also shows the melanopic irradiance corresponding to the melanopic EDI in Figure 5. Outdoor measurements of sunlight exposure were conducted on the rooftop of a five-story building. It is possible to measure tens of thousands of lx of sunlight during the daytime, and it is feasible to  
Figure 3: Spatial sensitivity of each channel of the circadian light meter. (**a**) V-filter attached photodiode for VIL measurement, (**b**) Mel-filter attached photodiode for melanopic EDI measurement, and (**c**) C-filter attached photodiode for CIL measurement.  
measure an exceedingly low VIL of \(\sim\)0.1 k at night. Although the proposed circadian light meter was able to measure the VIL, melanopic EDI, and CIL simultaneously, the non-standard CIL was excluded from the analysis because human factors research on the slight difference between the melanopic EDI and CIL were not conducted. The maximum VIL and melanopic EDI values during outdoor measurements were 53,609 \(\pm\) 1280 lx and 52,511 \(\pm\) 888 lx, respectively. However, the VIL and melanopic EDI values derived from the participants were 1580 \(\pm\) 702 lx and 1342 \(\pm\) 567 lx on average at noon, respectively. The participants were exposed to light with an average VIL of 158 lx and melanopic EDI of 141 lx after sunset (nighttime; 19:00-23:00). Even at midnight, they were also exposed to light with an average VIL of 70 lx and melanopic EDI of 61 lx. The ratio between the melanopic EDI and VIL of natural light and the light the participants were exposed to over time is shown in Figure S8 of the Supplementary Materials.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline  & & \multicolumn{2}{c}{**Conventional Light Meter**} & \multicolumn{3}{c}{**Circadian Light Meter**} \\  & & \multicolumn{2}{c}{**(CL-500A)**} & \multicolumn{3}{c}{**(This Work)**} \\ \cline{2-7}  & **VIL** & **Melanopic EDI \({}^{1}\)** & **CIL \({}^{1}\)** & **VIL** & **Melanopic EDI** & **CIL** \\  & **(lx)** & **(lx)** & **(lx)** & **(lx)** & **(lx)** & **(lx)** & **(lx)** \\ \hline White LED & 985.2 \(\pm\) 0.7 & 847.6 \(\pm\) 0.6 & 880.2 \(\pm\) 0.6 & 983.5 \(\pm\) 2.8 & 841.5 \(\pm\) 9.1 & 874.5 \(\pm\) 6.7 \\ (6500 K) & (0.0007) & (0.0007) & (0.0007) & (0.0029) & (0.0109) & (0.0077) \\ Halogen lamp & 113.7 \(\pm\) 0.5 & 17.6 \(\pm\) 0.3 & 19.1 \(\pm\) 0.3 & 122.0 \(\pm\) 0.6 & 19.9 \(\pm\) 0.3 & 20.7 \(\pm\) 0.3 \\ (0.0041) & (0.0151) & (0.0141) & (0.0053) & (0.0144) & (0.0143) \\ \hline \end{tabular} \({}^{1}\) Calculated value from the measured VIL and SPD of light.  
\end{table}
Table 1: Illuminance values according to the lighting sources measured ten times repeatedly under equal conditions. All data represent mean \(\pm\) standard deviation; values in parentheses represent coefficient of variation.  
Figure 4: **(a)** Photograph of the fabricated circadian light meter. The circadian light meter consists of three photodiodes with different filters attached (upper left: Mel-filter, upper right: V-filter, and lower: C-filter). **(b)** Photograph of a participant wearing the hat with the circadian light meter. The circadian light meter was attached to the hat visor through a parts output from a 3D printer.