## 4 Experimental Results and Discussion
Using the prototype optical module, the module transmitting illuminance was measured by rotating it in the \(\alpha\) and \(\beta\) directions around the center position of the CFL array plate. Then, the transmittance was calculated as a percentage of the reference illuminance. To measure the concentrated power efficiency, we used a PV cell with an effective area larger than 100 mm \(\times\) 100 mm. In the absence of the optical module, the reference generated power was measured in the 100 mm \(\times\) 100 mm PV area arranged perpendicular to the optical axis at 3 m in front and was set as the reference power for calculating the concentrated power efficiency. As shown in Figure 13a, as the size of the PV cell is larger than 100 mm \(\times\) 100 mm, a 100 mm \(\times\) 100 mm aperture plate was attached to the incident surface of the PV cell. The measured reference generated power was 22 uW. To measure the generated power with the proto-optical module, a PV cell with a 100 mm \(\times\) 5 mm aperture plate was attached to the incident surface of the PV cell, as shown in Figure 13b. An optical module was attached to the PV cell using a transparent encapsulant. Under these conditions, the generated power while rotating the proto-optical module in the \(\alpha\) and \(\beta\) directions around the center position of the CFL array plate was measured. In Figure 14, the measured module-transmitted illuminance and the measured generated power according to the rotation angles are shown as a percentage of each standard value. Comparing the results of the optical module transmittance according to the rotation angle shown in Figure 14a with the simulation results presented in Figure 12, it can be observed that a very similar trend is evident within the angular range of \(\mid\alpha\mid<35^{\circ}\) and \(\mid\beta\mid<3^{\circ}\). When both rotation angles \(\alpha\) and \(\beta\) were 0\({}^{\circ}\), the measured illuminance was 57 lx, corresponding to 53.8% of the measured reference illuminance,106 lx. Near \(\mid\alpha\mid=25^{\circ}\), the maximum transmittance of 55% was measured. As \(\mid\beta\mid\) increases, the transmittance continues to increase steadily, reaching up to 70%, which is similar to the maximum transmittance value shown in Figure 12b. For the generated power from the 5 mm \(\times\) 100 mm Si PV cell, the maximum value of 2.52 uW was measured when both rotation angles \(\alpha\) and \(\beta\) were 0\({}^{\circ}\), representing 11.5% of the reference generated power, 22 uW. Considering the maximum concentrated optical power efficiency, 21.4%, presented in Figure 12, this value is about 54% of the expected value. However, it was confirmed that the overall rotation angle-dependent tendency of the measured module transmittance and  
Figure 13: Apertured PV cell to measure generated electricity: (**a**) the apertured PV cell with a clear aperture of 100 mm \(\times\) 100 mm and (**b**) the apertured PV cell with a clear aperture of 5 mm \(\times\) 100 mm. the concentrated optical power efficiency are very similar to the results shown in Figure 12. There can be several reasons for the result that the generated power is lower than expected values from simulations. One major factor could be the inaccurate modeling of the applied illumination device and fabrication errors of the proto-optical module. Another significant factor is that, as illustrated in Figure 13b, the area of the aluminum electrode within the effective area of the PV cell attached to the CCPC end surface using encapsulant is relatively larger compared to the PV cell with the effective aperture of 100 mm \(\times\) 100 mm shown in Figure 13a. We judged that it induced about a 25% decrease in the generated power. In this study, additional investigations were conducted on the structure that could improve the concentration efficiency of the CCPC end surface. In the structure examined through design and experiment, the prism-shaped array at the exit surface of the lightguide was not treated as the reflective surface.