Photometric optimization and comparison of hybrid white LEDs for mesopic road lighting.

The photometric model for the mesopic luminous efficacy (LE) of hybrid white LEDs, including the radiant efficiency of both blue and red LEDs as well as the overall quantum efficiency of the phosphor layer or the quantum dot (QD) film, was developed. The optimal spectral parameters of integrated with quantum dots (QD-WLED), phosphor-converted white LED (pc-WLED) with red LEDs instead of red phosphor (pc/R WLED) for both color fidelity index (R) and color rendering index (R) above 70, 80, and 90 at correlated color temperatures of 2700-6500 K were obtained by maximizing the average LE of four road lighting standards. By comparing among pc-WLED, QD-WLED, and pc/R WLED, it was suggested that the pc/R WLEDs make strong candidates for mesopic road lighting.

Spectral optimization of phosphor-coated white LED for road lighting based on the mesopic limited luminous efficacy and IES color fidelity index.

The spectral optimization of phosphor-coated white LED (pc-WLED) with green and orange phosphors excited by blue chip for road lighting was investigated based on the mesopic limited luminous efficacy (LLE) and IES (the Illuminating Engineering Society of North America) color fidelity index (R). The average LLE of four road lighting standards of the USA and the UK decreases as R increases, but the optimal scotopic/photopic ratio increases slightly with R increases for a given correlated color temperature (CCT). The average LLE could reach the highest of 339  lm/W for R=70, 326  lm/W for R=80, and 309  lm/W for R=90 at CCT=5000  K.