## 3 Discussion
### Results of Different Diffuser Positions and Diffuser Contents in the Remote Phosphor LEDs  
As illustrated in Figure 3a, the CCT of the remote phosphor white LED was 6513 K when the TiO\({}_{2}\) diffuser content was 0; the CCT decreased to 2874 K when the diffuser content in the encapsulation layer was 0.8 wt.% and to 3869 K when the content in the phosphor layer was 0.8 wt.%. These findings can be explained as follows--the CCT of remote phosphor LEDs is determined by the ratio of the intensity of yellow light to that of blue light. The blue light emitted from LED chips excites phosphors to emit yellow light, and the Rayleigh scattering effect of the TiO\({}_{2}\) diffuser increases the amount of blue light and thus, leads to more yellow light. Hence, the intensity of the blue light decreases and that  
Figure 3: **(a)** The correlated color temperature (CCT), **(b)** the CCT P-V deviation, and **(c)** the luminous flux of the remote phosphor white LEDs for different TiO\({}_{2}\) contents. of the yellow light increases, thus reducing the CCT of the LEDs regardless of the diffuser position. This study determined that at a constant diffuser content, the CCT was lower in the case that involved diffuser in the encapsulation layer than in the case that involved a diffuser in the phosphor layer. This was engendered by the larger scattering volume of the diffusers in the encapsulation layer, leading to a greater Rayleigh scattering effect. Figure 3b demonstrates that adding the TiO\({}_{2}\) diffuser to the remote phosphor LEDs could improve the color temperature uniformity across the package. The diffusers could significantly reduce the CCT variance regardless of their position. The TiO\({}_{2}\) diffuser had more favorable effects in the encapsulation layer than in the phosphor layer, because the encapsulation layer was associated with the lowest CCT P-V deviation across all diffuser contents. At the diffuser content of 0.8 wt.%, the reduction rate of the CCT P-V deviation was approximately 82.15% in the phosphor layer [(\(1188-212\))/\(1188\)\(\times\)\(100\%\) = 82.15%], whereas that in the encapsulation layer was nearly 95.29% [(\(1188-56\))/\(1188\)\(\times\)\(100\%\) = 95.29%]. Thus, the diffusers in the encapsulation layer were associated with a better uniformity of CCT. The measurement results in Figure 3c reveal that the TiO\({}_{2}\) diffuser content influenced the lumen output of the remote phosphor LEDs. The TiO\({}_{2}\) diffuser increased the light output of a remote phosphor LED by more than 6.99% [(\(90.3-84.4\))/\(84.4\)\(\times\)\(100\%\) = 6.99%] when the inert diffuser content was 0.2 wt.% of the phosphor layer. In addition, the lumen output slightly increased because the effect of diffuser scattering could suppress the optical trapped modes with the rays inside the remote phosphor white LEDs having more than ten reflections from the Ag reflector cup. This was identified to be a significant light loss mechanism. Diffuser scattering led to the escape of light into free space, thus increasing the light extraction efficiency [18]. Then, the TiO\({}_{2}\) diffuser content increased and the lumen output decreased due to the excessive backward scattering and absorption of light by the encapsulant. As the TiO\({}_{2}\) diffuser content increased, the changes in the luminous flux increased, with the TiO\({}_{2}\) diffuser in the phosphor layer exhibiting a higher luminous flux than that in the encapsulation layer. This could be because the phosphor layer is thinner and can thus absorb less light.