Improving CRI and Scotopic-to-Photopic Ratio Simultaneously by Spectral Combinations of CCT-tunable LED Lighting Composed of Multi-chip LEDs

Important determinants for selecting outdoor lighting are the color-rendering index (CRI) and scotopic- to-photopic (S/P) ratio of the lighting units. The higher the S/P ratio, the better energy savings and visual performance. In this study, CCT-tunable LED lighting units were optimized and fabricated by spectral combination of red, green, blue, and yellow LEDs. The measured results for RGB LEDs provided S/P ratios of 1.55~2.58 and those of RGBY LEDs gave 1.46~2.46 to the correlated color temperatures (CCTs) ranging from 2700 K to 6500 K, with CRI values of over 80 at the same time.