Paul Jungwirth

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.