Laser-Driven Remote-Phosphor Searchlight Enabling Long-Range Illumination

This study experimentally evaluates two Ce3+ single-crystal phosphor configurations and implements a laser-diode-driven remote-phosphor (LDRP) module for high-intensity searchlight applications. Phosphor plates with thicknesses of 0.71 and 1.24 mm were characterized under excitation from a 450 ± 5 nm blue laser-diode array. Photometric, colorimetric, and 20-min temporal measurements were performed at selected drive currents between 1.2 and 2.2 A. At 2.0 A, the 0.71 mm phosphor produced approximately 12.5% higher luminous flux than the 1.24 mm phosphor, mainly because its shorter optical path increased the contribution of residual blue light. The 1.24 mm phosphor exhibited smaller current-dependent chromaticity variation. The 0.71 mm phosphor maintained stable output up to 2.0 A but fractured shortly after the application of 2.2 A. In contrast, the 1.24 mm phosphor remained stable at 2.2 A without measurable flux degradation during the 20-min measurement interval. The 1.24 mm phosphor was therefore employed in the integrated module. The module was characterized at 11.84 V and 2.202 A, corresponding to an electrical input power of 26.07 W. It produced near-white emission with chromaticity coordinates of (0.3123, 0.3434). Far-field goniophotometry measured a peak luminous intensity of 280 kcd with an FWHM beam divergence of 2.5°. The estimated on-axis illuminance was 1.12 lx at 500 m under clear atmospheric conditions; this value represents a theoretical propagation estimate rather than a direct field measurement. These results demonstrate the measured trade-off between luminous output and chromaticity stability, together with the different luminous-flux behaviors observed for the two evaluated configurations during the 20-min measurement interval.