Color temperature tunable phosphor-coated white LEDs with excellent photometric and colorimetric performances

The optimization model for the luminous efficacy (LE) of a correlated color temperature (CCT) tunable phosphor-coated white LED (pc-WLED) was developed. The optimal pc-WLEDs with green (498.7 nm, 70.0 nm), yellow (569.2 nm, 83.4 nm), and red (638.7 nm, 70.0 nm) phosphors excited by a blue chip (442.4 nm, 35.0 nm) could achieve a color fidelity index ($R_f$) of 97 and LEs of 118–127 lm/W at CCTs of 2700–6500 K for a radiant efficiency of the blue chip of 60% and a quantum efficiency of a phosphor layer of 90%. Compared to quantum dot WLEDs (QD-WLEDs), the LEs of the optimal pc-WLEDs are lower only by 2.7%–4.8% than the optimal QD-WLEDs at CCTs of 2700–6500 K, so that QD-WLEDs have only a slight advantage in terms of luminous efficacy for excellent color rendition. Four real pc-WLEDs with $R_{f}s$ of 96–97 and LEs of 93–106 lm/W at CCTs of 3037 K, 4081 K, 4951 K, and 6443 K were demonstrated.