## 3 Results
### Verification and Reproducibility of the Circadian Light Meter  
Through the ADC in the circadian light meter, the amplified voltage is converted into a digital electrical signal, which is transmitted to a data logger (a smartphone was used in this study), via the BLE module. To convert the voltage of the amplifier into the corresponding illuminance value, we established a conversion equation by matching the VIL, melanopic EDI, and CIL values obtained by the conventional light meter from the level of intra-daily sunlight exposure. Figure S5 shows the relationship between the actual illuminance and the amplified voltage from each photodiode. All fittings were performed using an orthogonal distance regression method to minimize the error between the actual illuminance and the illuminance estimated from the voltage by the circadian light meter. The voltage generated by the light incident on the photodiode took the form of the logarithmic function because a logarithmic amplifier was used. The circadian light meter used the fitted formula of the inverse function (exponential function) to express the illuminance levels according to voltage. In this process, because the lower measurement limit of the VIL of the conventional light meter was 0.1 k, any illuminance that was captured by the light meter and had a  
Figure 2: Relative responsivity of the fabricated circadian light meter. (**a**) VIL measurement channel (V-filter/photodiode), (**b**) melanopic EDI measurement channel (Mel-filter/photodiode), and (**c**) CIL measurement channel (C-filter/photodiode). The responsivity of each channel was calculated by weighting the transmittance of each filter to the responsivity of the photodiode. Cross-sectional view FE-SEM image with the backscattered electron detection mode of (**d**) V-filter, (**e**) Mel-filter, and (**f**) C-filter. The light and dark layers of the SEM images are TiO\({}_{2}\) and SiO\({}_{2}\) layer, respectively. The insets in each SEM image provide the photographs of fabricated the V-, Mel-, and C-filters. value below 0.1 lx was treated as 0.1 lx. The dynamic range of the system designed using a single gain resistor is very wide, from approximately 0.1 to 50,000 lx. Instruments designed and used for optical radiation measurements have several specific parameters [24]. The \({f_{1}}^{\prime}\) of the V-filter attached photodiode was 13.1% (Figure 2). However, the \({f_{1}}^{\prime}\) values for the Mel- and C-filter attached photodiode were 166.3% and 176.8%, respectively, it is natural that a greatly large error occurs because the \({f_{1}}^{\prime}\) value is calculated using \(V(\lambda)\); the \({f_{1}}^{\prime}\) values of the melanopic EDI and CIL channels calculated using their corresponding action spectrum rather than \(V(\lambda)\) are 19.5% and 25.3%, respectively. In addition, because the three types of filters used in this study are interference filters, the greatest effect can be seen only when light passes through the filter perpendicularly. In other words, the interference filters can have unintended consequences in off-axis irradiance [22]. As shown in Figure 3, it can be seen that the relative amplitude of the off-axis irradiance is lower than the cosine distribution. The \({f_{2}}\) of VII, melanopic EDI, and CIL measurement channels were 24.4%, 22.2%, and 25.9%, respectively. To evaluate the reproducibility of the circadian light meter, we used a conventional white LED with a CCT of 6500 K and a halogen lamp. Table 1 summarizes the illuminance values obtained by ten iterations of the circadian light meter and conventional illuminance spectrophotometer (CL-500A). When repeatedly measuring the white LED with a CCT of 6500 K using the conventional light meter and the proposed light meter, the measured VILs (mean \(\pm\) SD) were 985.2 \(\pm\) 0.7 lx and 983.5 \(\pm\) 2.8 lx, respectively. Meanwhile, the average VIL values, measured repeatedly, of the halogen lamp were 113.7 \(\pm\) 0.5 lx (conventional light meter) and 122.0 \(\pm\) 0.6 lx (circadian light meter).