## 4 Experimental Results and Discussion  
The solar radiation spectrum data used in the design of the optical module does not match the local solar radiation conditions in the laboratory, and accurate radiation spectra considering the local weather conditions are not known. Therefore, to experimentally measure the through-module transmittance and power generation, a high-power white LED illumination device was used. In this study, a high-power white light LED with a color temperature of 6500 K and a radiant output of 2420 lm, CXB1520 from Cree LED (Durham, NC, USA), along with two lenses, was used for illumination. Figure 11 illustrates the applied LED radiation spectrum and the experimental concept for measuring the transmittance and power generation of the fabricated module. The emitted light from the illumination device equipped with converging lenses is incident on the fabricated optical module placed 3 m ahead. In the experiment, we used the monocrystalline p-type silicon photovoltaic (Si PV) cell, SCM 5 WE-6V from Solarcenter (Gimpo-si, Republic of Korea). It was attached to the CCPC end surface, which has an area of 5 mm \(\times\) 100 mm, using a transparent encapsulant, Sylgard-184 from DOW (Midland, MI, USA). Before the experiment, considering the fabrication deviations of the optical module and experimental  
Figure 10: Transmittance through the module and the concentrated optical power efficiency on the CCPC end surface according to variation in the incidence angle of the sun, considering fabrication error of the CFL module: (**a**) result of variation in \(\alpha\) and (**b**) result of variation in \(\beta\). Figure 9: Assembled optical module prototype. conditions, the through-module transmittance and the concentrated power efficiency on the CCPC end surface and the incident surface of the Si PV cell were predicted. In the results shown in Figure 12, the illumination device consisting of an LED light source and two lenses as presented in Figure 11 were considered, and the thickness of the transparent encapsulant was set to 0.1 mm. Since a commercially available illumination device was used, the specifications of the two lenses were not precisely known, so we modeled them based on data measured by a surface profiler. Comparing with the results shown in Figure 10, it can be observed that, on average, the transmittance and the concentrated power efficiency decreased by approximately 3.8% and 2.4%, respectively, for the rotation angle \(\alpha\). However, the overall trends of transmittance and the concentrated power efficiency were very similar. For the rotation angle \(\beta\), both parameters are more sensitively changed compared to the results shown in Figure 10. This is because, for the approximate solar source of 16,205 mm, the incident angle of all light incident on the module is close to 0\({}^{\circ}\). However, under experimental conditions, considering a distance of 3 m between the illumination device and the module, the incident angle  
Figure 11: Experimental concept for measuring the through-module transmittance and the generated electrical power using the concentrated solar power in Si PV cell. Figure 12: Transmittance through the module and the concentrated optical power efficiency on the CCPC end surface and the incident surface of the Si PV cell according to variation in the incidence angle of the sun, considering experimental conditions: (**a**) result of variation in \(\alpha\) and (**b**) result of variation in \(\beta\). ranges from 0\({}^{\circ}\) to 1.9\({}^{\circ}\), and the sensitivity of the rotation direction \(\beta\) is higher than that of the rotation direction \(\alpha\). To experimentally measure the module transmittance and compare the simulation results, we first measured the reference illuminance at a distance of 3 m in front of the illumination device in the absence of the fabricated optical module. The measured reference illuminance at 3 m in front of the illumination device was 106 lx.