## 3 Discussion
### Optimum Design of the Remote Phosphor LED  
Because TiO\({}_{2}\) diffuser-loaded encapsulation in the remote phosphor LEDs generated not only light-scattering effects but also light absorption to reduce luminous flux, we sought the optimum conditions for enhancing the angular CCT uniformity and maintaining a higher level of luminous output. Accordingly, the TiO\({}_{2}\) diffuser content of 0.2 wt.% in the phosphor layer was determined to be an adequate condition for obtaining a lower CCT P-V deviation and a higher luminous flux. However, this would concurrently reduce the CCT from 6513 K to 5524 K of remote phosphor white LEDs. Therefore, to preserve the CCT in the range of 6500 \(\pm\) 100 K, the phosphor content in the phosphor layer of the remote phosphor white LEDs must be adjusted. After the experiments, we adjusted the phosphor content from the original 17.0 wt.% to 16.0 wt.% and the CCT of the remote phosphor LED was changed to 6516 K. Figure 4a shows the changes in the CCT resulting from changes in the content of the silicon during the mixing of the phosphor with the TiO\({}_{2}\) diffuser content of 0.2 wt.%. Figure 4b shows the electroluminescence spectra of the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED at a driving current of 350 mA. The relative spectrum has two specific peaks, centered at 460 and 570 nm. The results in this study utilized a blue LED chip and phosphor to produce white light. The angular CCT distribution of the non-diffuser and TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor white LEDs was measured, as illustrated in Figure 5. It is clear that the angular CCT deviation of the non-diffuser remote phosphor LED was improved by 31.82% [\((1188-810)/1188\times 100\%=31.82\%\)] by the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED in the range of \(-70^{\circ}\) to \(70^{\circ}\). The non-diffuser remote phosphor LED had a larger angular CCT deviation, which was due to the longer optical path for the high angles, where the blue photons can be converted more easily by the phosphor particles than the normal directions, limiting the extraction of blue light at this angle and consequently leading to ineffective color mixing of blue and yellow light. The TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED was observed to have a smoother angular CCT distribution, because the TiO\({}_{2}\) diffuser could provide an effective scattering capability to improve the ratio of yellow to blue light at large angles. The CCTs for both remote phosphor LEDs were almost the same (6513 and 6516 K) at a driving current of 350 mA. To further understand the optical characteristics of the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED, we measured the current-depe  
Figure 4: (**a**) Dependence of CCT on the phosphor content for the remote phosphor white LEDs with the TiO\({}_{2}\) diffuser content of 0.2 wt.% in the phosphor layer, (**b**) Electroluminescence spectra of the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED at a driving current of 350 mA. Figure 5: Angular CCT distribution of non-diffuser and TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LEDs. calculated the normalization of luminous efficacy. As presented in Figure 6a, the luminous flux of the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED slightly increased by 8.65% [(91.7 - 84.4)/84.4 \(\times\) 100% = 8.65%], at a driving current of 350 mA, compared with the non-diffuser remote phosphor LED. As shown in Figure 6b, the normalization of luminous efficacy of the TiO\({}_{2}\) diffuser-loaded encapsulation remote phosphor LED slightly increased by 7.81% [0.801 - 0.743)/0.743 \(\times\) 100% = 7.81%], at a driving current of 350 mA, compared with the non-diffuser remote phosphor LED. The slopes of the normalization efficacy curves have similar trends for the two samples, this is because they use the same LED chip and phosphor.