Static ceramic phosphor assemblies for high-power high-luminance SSL-light sources for digital projection and specialty lighting

Laser pumped phosphor (LPP) technology has started to replace high intensity discharge lamps in digital projectors. LPP technology is typically based on garnet phosphors that are excited with blue laser diodes at 445 – 465 nm. The luminance of LPP light sources can well surpass 1000 cd/mm² and thus address high luminance applications that could not benefit from the advantages of solid state lighting (SSL) so far. Due to the recent cost down of blue laser diodes, digital projectors with LPP light sources that make use of fast spinning phosphor wheels and laser powers >100 Watts are now widely commercially available. Another commercially available application of LPP technology are laser headlights. To avoid moving parts, laser headlights make use of static phosphor assemblies, but they operate at only a few Watts of laser power. A static phosphor assembly consists of a ceramic phosphor that is bonded onto a heat spreader. Due to their good thermal and optical properties, static ceramic phosphors are excellent light converters even at higher powers. They enable high luminance light sources with a luminous flux that is far beyond the flux needed for car headlights. Static converters will also improve the performance of light sources for microscopy, machine vision and any other etendue limited specialty lighting application. We investigate factors that determine the achievable power and luminance such as irradiance limit, conversion efficacy, spot confinement and cooling. Experimental and numerical results are presented.