# Spectra Prediction for WLEDs with High TLCI
## 3 Results and Discussion  
In this study, a blue LED chip, green phosphor, and red phosphor were used. Firstly, three LEDs packaged with green phosphor and three LEDs packaged with red phosphor were fabricated, and we measured the spectrum of the single-phosphor LEDs. Three WLEDs were fabricated to reduce the errors and average the temperature rise. The measured spectra are shown in Figure 3. From Section 2, using Equation (2), the conversion  
Figure 5: Overlapping between red phosphor excitation spectrum and green phosphor emission spectrum. (Excitation spectrum is provided by Raypower Optoelectronics (Suzhou) Co., Ltd., Suzhou, China). efficiencies of the green phosphor and red phosphor were 0.79 and 0.44, respectively, which are \(Q_{G}=0.79\) and \(Q_{R}=0.44\). Then, we measured the spectra of two kinds of LEDs mentioned earlier under different currents, and the peak wavelength of the emission spectrum changed with the driving current, as shown in Figure 6. Figure 6a shows the change in the emission spectrum of the blue chip with the driving current; the driving current increases from 1A to 4A, and the peak wavelength decreases from 447 nm to 445 nm. Figure 6b shows the change in the green phosphor emission spectrum with the drive current, which increases from 1A to 4A, and the peak wavelength increases from 523 nm to 525 nm. Figure 6c shows the change in the emission spectrum of red phosphor with the drive current, which increases from 1A to 4A, and the peak wavelength decreases from 645 nm to 640 nm. Figure 6d shows the results with a linear fit. The average temperature rise of the LED packaged with green phosphor at 1A, 2A, 3A, and 4A was 21.12 \({}^{\circ}\)C, 21.61 \({}^{\circ}\)C, 22.25 \({}^{\circ}\)C, and 23.14 \({}^{\circ}\)C, respectively. As we all know, as the drive current increases, the LED modules' temperature also increases. The average temperature rise of the LED packaged with red phosphor at 1A, 2A, 3A, and 4A was 21.74 \({}^{\circ}\)C, 22.01 \({}^{\circ}\)C, 22.65 \({}^{\circ}\)C, and 23.55 \({}^{\circ}\)C, respectively. This is due to the lower conversion efficiency of red phosphorescent powders. In order to make the peak intensity of the phosphor roughly equal to the peak intensity of blue light, red phosphor was more thickly applied. Fitting the peak wavelength shift reveals that \(k\) is \(-0.95\), 0.65, \(-1.30\), and \(b\) is 0.5, \(-0.5\), and 1, respectively. As shown in Figure 6, as the driving current increases, it is interesting that blue and red light undergoes a blue shift, which is related to the material, while green light undergoes a red shift, which is related to the material, too. The reason for the peak wavelength blue shift of the LED chip is the strong polarization effect of the multi-quantum-well region [28], but the causes of the peak wavelength shift of the phosphors are related to charge distribution and crystal field changes [29]. Subsequently, we packaged three dual-phosphor WLEDs (green phosphor: 0.20 g; red phosphor: 0.03 g; A glue: 0.025 g; B glue: 0.025 g) at a CCT of 5860 K. The weight percent (wt%) of green phosphor is 74.43%, and the weight percent of red phosphor is 10.71%. We measured the spectrum of the WLEDs and fitted the spectrum to calculate the proportion of green light reabsorbed by red phosphor under the currents of 1A, 2A, 3A, and 4A, respectively. The average temperature rise of the WLEDs at 1A, 2A, 3A, and 4A was 22.48 \({}^{\circ}\)C, 22.95 \({}^{\circ}\)C, 23.66 \({}^{\circ}\)C, and 24.55 \({}^{\circ}\)C, respectively. The results of the spectral fit are shown in Figure 7. Figure 7a-d show the fitted spectrum for different \(W_{G-R}\) and  
Figure 6: Spectrum under different driving currents. (**a**) Spectrum of the chip. (**b**) Spectrum of green phosphor. (**c**) Spectrum of red phosphor. (**d**) Fitting result of the spectral shift. Then, according to Equation (5), we simulated the spectrum under different CCTs by varying the ratio of green and red phosphors.