High brightness light sources based on LD-pumped luminescent converters and LED-pumped luminescent concentrators

Although LEDs have penetrated successfully in many lighting domains, high brightness light source applications are still suffering from their limited luminance. High power LEDs are generally limited to less than 100 Mnit (10⁸ lm/m²sr), while dedicated devices for projection may achieve pulsed peak luminance values up to 200 Mnit for phosphorconverted green. For high luminous flux applications with limited etendue, like in stage or architecture spot lighting or in front projection, in the beam only very modest luminance values can be achieved with LEDs compared to systems based on discharge lamps. In this paper we evaluate light engine concepts based on static luminescent converters pumped by blue laser diodes, and concepts based on luminescent concentrators pumped by blue LEDs. Both concepts break through the flux and brightness requirements for these applications by enabling luminance values that are a factor five to ten higher than what can be achieved with LEDs. With continuous wave irradiation of a 10 mm² static converter by multiple laser diodes, 47 klm yellow-green emission was achieved at 1.5 Gnit source luminance, or 40 klm @1.2 Gnit in a collimated beam. With yellow-green light concentrator modules, 16 klm yellow-green emission was achieved at 1.2 Gnit collimated beam luminance. Thermal conditions are much more relaxed in luminescent concentrator modules than for static laser diode (LD) pumped converter systems. The High Lumen Density (HLD) LED-based luminescent concentrator, with its advantage of scalability in both flux and luminance, enables breakthrough performance in projection systems and in a wide variety of other applications. Laser-pumped converters, on the other hand, easily scale in flux proportional to their source size at constant luminance. They show very high flux capability and comparable brightness, enabling scope extension with extremely high flux solid state light sources.