## 3 Results
### Spectral Composition Strategies with Tunable Spectral Characteristics  
We constructed a series of spectra at the range of CCT from 3000 to 7000 K in both cases of B:Y ratio. [PERSON]'s formula [20] was adopted to calculate CCT, where x and y refer to the chromaticity coordinates in the CIE 1931 chromaticity diagram. The color rendering index R\({}_{\text{a}}\) is also calculated using the calculator proposed in the database of IES TM-30-15. \[\text{CCT}\ =\ -449\cdot\text{n}^{3}+3525\cdot\text{n}^{2}-6823\cdot\text{n}+5520.33,\ \text{where n}=\frac{\text{x}-0.3320}{\text{y}-0.1858} \tag{5}\]  
Figure 4a,b shows the spectra under the LER-maximizing strategy. The spectral characteristics corresponding to the spectra in Figure 4a,b are listed in Table 1.  
Figure 3: Melanopic effeciency of radiation (MER) and luminous efficiency of radiation (LER) as functions of \(\lambda_{2}\) and \(\Delta\lambda_{2}\) at different B:Y ratios: (**a**) MER and (**b**) LER with the peak wavelengths of phosphor (\(\lambda_{2}\)) ranging from 520 to 600 nm and the full widths at half maximum (FWHMs) of phosphor (\(\Delta\lambda_{2}\)) ranging from 100 to 200 nm at a blue:yellow intensity ratio (B:Y ratio) of 1 to 0.7, (**c**) MER and (**d**) LER with \(\lambda_{2}\) ranging from 520 to 620 nm and \(\Delta\lambda_{2}\) ranging from 100 to 200 nm at a B:Y ratio of 0.6 to 1. For all the spectra, the peak wavelength and FWHM of the blue LED are fixed at: \(\lambda_{1}=450\) nm, \(\Delta\lambda_{1}=22\) nm. The asymmetric factor (AF) of phosphor is 0.3 and \(-0.05\), respectively. The values of the spectral characteristics reveal that to maximize LER, \(\Delta\lambda_{2}\) approximately reaches the minimum we set (100 nm) at various CCTs. The increase in CCT mainly depends on the variation of \(\lambda_{2}\) towards a short wavelength. As for the B:Y ratio, it tends to minimize the distribution of the blue LED. These results suggest that a low intensity ratio of blue LED and the FWHM of phosphor are beneficial for LER. Under the LER-maximizing strategy, LER reaches a peak of 390.0 lm/W at 6000 K for B:Y Ratio \(>1\), whereas the values of LER are all over 410 lm/W for B:Y ratio \(<1\). Reducing the blue light distribution is more likely to obtain a higher LER at each CCT, of which high LER and low MER make it a better strategy in low circadian effect lighting at CCT below 4000 K. However, the color rendering index R\({}_{a}\) in this case decreases sharply at a higher CCT due to the excessive reduction of blue intensity. Therefore, different combinations of spectral characteristics correspond to tunable LED performance even at the same CCT. Figure 5 shows LER and MER with different B:Y ratios at various CCTs under the LER-maximizing strategy (the blue and red solid lines with solid square markers) and the MER-maximizing strategy (the blue and red solid lines with hollow square markers), respectively. It reveals that the values of MER are quite close under these two strategies, and both increase with CCT. Furthermore, in both Figure 5a,b, MER under the LER-maximizing strategy almost overlaps with the maximum MER at a higher CCT, no matter what the intensity of blue light is. This suggests that a decrease in MER necessarily leads to a decrease in LER. Hence, we further explored the trade-off between MER and LER in circadian lighting and the corresponding spectral composition, which is discussed in the next section.