# Spectra Prediction for WLEDs with High TLCI
## 3 Results and Discussion
It is well known that we could fix the ratio of green and red phosphors and obtain the spectra of different CCTs by adjusting the thickness of the phosphor layer. However, changes in the thickness would seriously alter the temperature of the chip, thus affecting the light efficiency of the LED. Therefore, it is better to change the ratio of green and red phosphors to obtain the spectra of different CCTs. We calculated the TLCI of the spectrum according to the method in this reference [13]. When the drive current is 2A, the color coordinates of LEDs with a TLCI greater than 90 are shown in Figure 9. Admittedly, the correlated color temperature lacks color adaptation considerations [30; 31]. Therefore, we chose \(duv<0.02\) as another indicator to limit the distance from the color coordinates to the Planckian locus. The results show that the chip and phosphors used in this study can package WLEDs with a TLCI \(>\) 90 from 2650 K to 9000 K.  
Finally, to verify the model, we packaged four other kinds of WLEDs for other CCTs. Each one has three WLEDs with a similar CCT. Figure 10 shows the spectra of the experimental measurements and simulation results at 2A. The measurement results show that the CCTs of the WLEDs are 3114 \(\pm\) 27 K, 4178 \(\pm\) 34 K, 5000 \(\pm\) 55 K, and 6990 \(\pm\) 37 K, respectively. Figure 10a shows the predicted and experimental spectra and temperature rise at 3114 K, Figure 10b shows the predicted and experimental spectra and temperature rise at 4178 K, Figure 10c shows the predicted and experimental spectra and temperature rise at 5000 K, and Figure 10d shows the predicted and experimental spectra and temperature rise at 6990 K. We conducted a correlation analysis to evaluate the similarity between the predicted and experimental spectra, aiming to test the spectral resemblance. The results revealed strong positive correlations between the predicted and experimental spectra, as indicated by high Pearson correlation coefficients of 0.99511, 0.96875, 0.9476, and 0.91305 (\(p<0.0001\)). The Spearman correlation coefficients were also significant at 0.99277, 0.94436, 0.93312, and 0.95551 (\(p<0.0001\)), respectively. These findings confirm that the predicted spectrum bears substantial similarity to the experimental spectrum in terms of their spectral characteristics. Furthermore, the consistent trend of spectral line variations implies a high level of agreement between the two datasets. As shown in Figure 10, despite differences in the details, the simulated spectra still represent the experimental spectra well. The lower the CCT is, the smaller the concentration of the red phosphor is. Since the conversion efficiency of red phosphors is lower than that of green phosphors, the temperature rise of the WLEDs increases slightly with the decrease in the CCT. However, in this study, the temperature rise of the dual-phosphor WLEDs is basically maintained at the same level, and the spectral shift is small. Figure 9: Prediction of chromatic coordinates of WLEDs with \(TLCI>\) 90. (\(duv<0.02\)). The detailed results are listed in Table 1. The results demonstrate that the simulation results provide rather good predictions, and the maximum difference of the TLCI between the measurements and the model is approximately 1.93%. To show the difference between the predicted and experimental spectra more clearly, we calculated the color coordinates of each spectrum. The color coordinates are shown in Figure 11. As shown in Figure 11, in addition to the color coordinates at 5860 K used for fitting, the color coordinates of the predicted spectrum at other color temperatures also agree well with the experimental values. The predicted spectral color coordinates almost overlap with the experimental measured spectral color coordinates, indicating that the model could predict the spectrum of dual-phosphor LEDs well. Figure 10: Experimental and simulated spectra and temperature rise of WLEDs. (**a**) 3114 K, (**b**) 4178 K, (**c**) 5000 K, and (**d**) for 6990 K. All spectra were measured at 2A.