High-efficiency, low-speckle contrast white laser lighting via multi-stage scattering and photon recycling

Abstract

Lighting consumes > 10% of the global electricity. White laser lighting, utilizing either direct color mixing or phosphor-conversion, can potentially boost the efficiency well beyond existing light emitting diodes (LEDs) especially at high current density. Here we present a compact, universal packaging platform for both laser lighting schemes, which is simultaneously scalable to wavelength division multiplexing for visible light communication. Using commercially available laser diodes and optical components, low-speckle contrast ≤ 5% and uniform illumination is achieved by multi-stage scattering and photon recycling through a mixing rod and static diffusers in a truncated-pyramidal reflective cavity. We demonstrate a high luminous efficacy of 274 lm/Wo for phosphor-converted laser lighting and 150 lm/Wo for direct red-green-blue laser mixing, respectively, in reference to the input optical power. In the former case, the luminous efficacy achieved for practical lighting is even higher than most of the previous reports measured using integrating spheres. In the latter case of direct laser color mixing, to our best knowledge, this is the first time to achieve a luminous efficacy approaching their phosphor-conversion counterparts in a compact package applicable to practical lighting. With future improvement of blue laser diode efficiency and development of yellow/amber/orange laser diodes, we envision that this universal white laser package can potentially achieve a luminous efficacy > 275 lm/We in reference to the input electrical power, ~ 1.5x higher than state-of-the-art LED lighting and exceeding the target of 249 lm/We for 2035.