Spectral optimization of color temperature tunable white LEDs with red LEDs instead of phosphor for an excellent IES color fidelity index

The optimal spectral parameters and photometric performances of white LEDs with red LEDs instead of phosphor (pc/R-WLEDs) for the color fidelity index (Rf) above 97 at correlated color temperatures (CCTs) of 2700 K to 6500 K have been obtained based on the luminous efficacy (LE) model. We have first reported four real pc/R-WLEDs with Rfs of 96–97 and LEs of 120–124 lm/W at CCTs of 2969 K, 4468 K, 5682 K, and 6558 K by using blue (448 nm) and red (650 nm) LEDs, as well as green (507 nm) and yellow (586 nm) phosphors. As compared with phosphor-converted white LEDs (pc-WLEDs) as well as quantum dots white LEDs (QD-WLED), it was found that the pc/R-WLEDs, not the QD-WLED as widely expected, make strong candidates for excellent color rendition, especially in the low color temperature range, for replacing current pc-WLEDs in the future.