Novel strategy to optimize luminance for phosphor-converted laser lighting

Phosphor-converted white laser diodes (pc-wLDs) are a new development in high-luminance white light sources. However, the optical design and material evaluation methods of the pc-wLD system have been facing a long-neglected problem which is associated with the lack of understanding the selecting principle of the incident laser spot area (ILSA). The ILSA design affects the optical/thermal load on the phosphor(s) and the emitting area and beam quality of the luminaire. Here, we present a comprehensive evaluation of canonical phosphors (Y3Al5O12:Ce³⁺ and (Sr,Ca)AlSiN3:Eu²⁺) on the optical/thermal properties, using an excitation laser with wide range laser power (0.1 W–16 W) and ILSA (0.023 mm²–4.780 mm²). The relationship between the lighting parameters (luminous efficacy, luminous flux and luminous exitance), temperature increase and the ILSA is elucidated, showing that the optimal ILSAs for different phosphors can be significantly different: the Y3Al5O12:Ce³⁺-based light source attains the highest luminous exitance with ILSA of 0.41 mm²; in contrast, the (Sr,Ca)AlSiN3:Eu²⁺-based light source attains highest luminous exitance with ILSA of 0.023 mm². These new finding will not only impact the material selection and optical design of pc-wLD, but also provide new strategy to optimize the lighting parameters of pc-wLD.