The luminous efficacy of Ce:Y₃Al₅O₁₂ (YAG) glass-ceramic (GC) phosphor increased with the increasing crystal size of precipitated Ce:YAG, while the light scattering coefficient decreased. This increase in luminous efficacy can be attributed to the decrease in light scattering loss owing to the decrease in light scattering coefficient with increasing Ce:YAG crystal size. According to Mie scattering theory, the reason for the decrease in the light scattering coefficient is the decrease in light scattering cross-section per unit volume with increasing Ce:YAG crystal size.