Matthijs H. Keuper

Remote phosphor LED modules for general illumination: toward 200 lm/W general lighting LED light sources

Phosphor converted white LEDs are becoming more and more attractive for general lighting applications because of the steadily increasing luminous efficacy numbers reported by LED-suppliers. Despite these high numbers, a further significant improvement step can be made when a low-to-medium brightness (<500 kCd/m2) source is acceptable. The wall plug efficiency of a blue LED is generally better than that of a conventional white LED made from the same die. To take full advantage of this, we have developed medium-brightness LED-modules (~150 kCd/m2) for general lighting in which the phosphor is applied remote from the blue LEDs. By direct comparison with modules in which conventional high power white LEDs with almost identical dies are applied, we have shown that on system level the remote phosphor modules can have up to 50% better efficacy. Using a downlight module as a carrier, we have shown that in the relevant color temperature range of 2700 to 4000K a high CRI (>80) can be obtained in combination with a high luminous efficacy, while the optical efficiency of the module can be over 85%. A module efficacy of over 100 lm/W at 4000K with CRI 80 seems to be within reach, with a long-term expectation of over 180 lm/W. The remote phosphor LED modules deliver well homogenized white light with a Lambertian radiation profile. They are ideal for general illumination, as they combine glare reduction with high system efficacy and enable high optical efficiencies of the luminaries. The RP modules enable forward compatibility by well defined interfaces and optical properties that are decoupled from the actual performance, form factor and number of LEDs in the module. The Philips Fortimo downlight system is based on this remote phosphor concept, featuring forward compatibility and a total system efficacy (including driver) of over 60 lm/W under operating conditions using currently available Luxeon Rebel emitters.

Color-consistent LED modules for general lighting

During the last few decades the efficacy and luminous flux of LEDs have developed fast. Also the color quality of white LEDs and LED illumination systems has improved considerably. Thanks to the performance improvements and the continuously declining cost per lumen, it is now possible to create LED lighting systems with high luminous fluxes that can be applied in downlights for general lighting and in spot lights for accent lighting. One of the important requirements on lighting systems in indoor lighting applications is the color consistency. For all systems the chromaticity, or color point, of the light should be the same, i.e. within well-defined small tolerance areas. For down lighting, LED modules with high optical efficiency have been developed based on the concept of mixing light from multiple LEDs and luminescent materials, and emitting the mixed light through a translucent window. This concept is ideal for down lighting and other general illumination applications since it enables the design of luminaires with high optical efficiencies and low glare. In addition, it enables high color uniformity and excellent color consistency between modules. The module concept enables forward compatibility by well-defined interfaces and optical properties that are decoupled from the actual performance and number of LEDs. In this paper the properties with respect to color consistency of the various concepts will be discussed. By applying a phosphor remote from the blue LEDs, we have developed mediumbrightness (100-200 kCd/m2) LED-modules with high system efficacy. This is the basis of the Philips Fortimo downlight system. Based on mixing of multiple colors, the color tunable Lexel downlight module has been developed. The systems comprising multiple LED colors have feedback loops to comply with color consistency requirements. In all systems a color consistency within 5 SDCM is achieved.