Study on color-tunable phosphor-coated white light-emitting diodes with high S/P ratios

In this study, we have investigated the trade-off between the color rendering index (CRI, Ra) and the scotopic/photopic ratio (S/P) for color-tunable phosphor-coated white light-emitting diodes (LEDs) at two CRI limitations (Ra ≥ 70 and Ra ≥ 96). First, luminescent spectra measurements have been conducted to determine experimental results of Ra and S/P under various correlated color temperatures (CCTs). Then, a nonlinear programming method has been adopted for the optimization of Ra and S/P by varying spectral shapes through adjusting spectral parameters, such as peak wavelengths, full-width at half-maxima, and relative intensities. Therefore, polynomial curves of optimal S/P versus CCT at two Ra limitations have been discovered, enabling users to obtain optimal S/P under arbitrary CCTs within [2700 K, 6500 K]. In addition, a comparison study between the present work and our previous work has also been conducted at Ra = 70, and a fair agreement of optimal S/P has been observed.