## 3 Experimental Details and Results for Phosphor-Converted White Light Systems  
The procurement of commercial phosphor powders of average diameter of 15 microns was made from Zhuhai Hanbo Co., Ltd. (Zhuhai, China) The red phosphor (RP) SrAlSiN\({}_{3}\): Eu\({}^{+2}\) has a quantum efficiency of approximately 82.3% [48]; the green phosphor (GP) SrBaSiO\({}_{4}\): Eu\({}^{+2}\) has a quantum efficiency of 88.6% [49], and the yellow phosphor (YP) Y\({}_{3}\)Al\({}_{5}\)O\({}_{12}\): Ce\({}^{+3}\) has a quantum efficiency greater than 85% [50]. The initial step involved combining YP with transparent optical adhesive (NOA61-MIL-A-3920 (Norland Products Inc., South Brunswick Township, NJ 08831, USA)) in a proportion of approximately 7:2. Subsequently, this mixture was applied onto a transparent glass slide measuring 2.5 cm \(\times\) 2.5 cm using the screen-printing process. The slide was subjected to UV irradiation for 10 min to remove moisture. Similarly, the two remaining layers were built and activated for a few seconds remotely using a 6 W blue LED placed 1 cm apart. Moreover, these slides were stacked together to form a three-layer combination and then activated remotely using the same source. A portable spectroradiometer (Lisun-6000 (LISUN ELECTRONICS (SHANGHAI) CO., Ltd., Shanghai, China)) measured the CRI, CCT, and CIE 1931 parameters. The integration time for the measurements was set to 1 s.  
Figure 1a shows the fitted spectrum of single phosphor-coated slides with GP, RP, and YP. It was observed that most of the down-converted photons are surrounded near the peak-emission wavelength of 521 nm, 621 nm, and 552 nm, corresponding to the activator cations of GP, RP, and YP, respectively. Figure 1b shows the spectrum of a three-layer combination of these slides stacked together and excited with the same source again. A large band of down-converted frequencies is observed when GP is placed first at the optical axis, followed by YP and RP. However, the spectrum is not flat compared to sunlight (visible region) due to thermal and PL quenching in multi-layered structures. Figure 1d,e shows CRI, CCT, and CIE coordinates (in parentheses) associated with Figure 1a,b, respectively. A lamp is made to add seven LEDs using a reflector and diffuser assembly to create a broadband spectrum to overcome thermal quenching and limited optical bandwidth. The diffuser reduces optical power by 30% at a distance of 30 cm. These seven LEDs of six colors (green used twice) are mounted equidistantly on a heat sink in a side-by-side (co-planar) ring structure. Figure 1c compares the spectrum of DL to conventional WL, and Figure 1f shows the CRI, CCT, and angular uniformity of DL. Figure 1: (a) Spectral distribution of green, red, and yellow phosphor-coated slides using blue LED as an excitation source (Gaussian fitted to report FWHM); (b) multi-layer stacking configuration of  
these phosphor-coated slides using same source; (**c**) comparison of resultant broadband spectrum of designed lamp (DL) composed of side-by-side mounting seven LEDs with that of general white LED (WL); (**d**) and (**e**) show color-rendering index (CRI), correlated color temperature (CCT), and CIE 1931 chromaticity coordinates (in parentheses) associated with Figures 1a and 1b, respectively; (**f**) angular uniformity of CRI and CCT of the DL. LEDs are of 2B3C-3W, surface mount device type, with 300 lumens with forward current of 300 mA, having dimensions 12 mm \(\times\) 12 mm, tolerance of \(\pm\)0.2 mm, max power dissipation of 4560 mW, forward voltage in the range 9-11.4 V, and maximum reverse current of 20 \(\mu\)A with half angle 70 degrees. All the properties were reported in the datasheet at 25 degrees temperature. Figure 2a shows the PL spectrum of six LEDs with a peak wavelength of blue (451 nm), pink (612 nm), yellow (601 nm), white, red (632 nm), and two green (523 nm) lights. Two green LEDs were used to improve CIE color coordinates. Figure 2b compares the difference in R1-R15 color patches responsible for CRI and special CRI.