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The unique features of light emitting diodes (LEDs) such as intrinsic color generation and relative low temperature operation enable completely new lighting concepts. The ongoing increase in performance of LEDs reaching efficacy levels of more than 30 lm/W for illumination grade white light with the promise of reaching over 75 lm/W makes them also applicable for higher luminous applications such as spot and flood lighting, accent lighting and architectural lighting. For the new lighting feature of ambiance creation, which requires at least variation of the color temperature of the light and preferably also selection of more saturated colors, LEDs are ideally suited. In this paper we report on the overall system aspects to color variable LED spot lighting and on the performance of prototype spot modules. Mixing of the light is performed within the lighting module by a combination of dense packing of red/amber, green and blue emitting dice, and light collimation with facetted optics and small angle diffusion, resulting in a homogeneous appearance of the light source and a color point inhomogeneity Δu'v' in the beam (>90% of total flux) of less than 0.01. A color rendering index (Ra8) of over 80 can be obtained over a large temperature and color temperature range with the 3-color system for a specific combination of 5 nm wide wavelength bins. In the prototype spot modules, between 9 and 14 dice are mounted on a common substrate and integrated with the primary collimating optics that is based on total internal reflection. Nominal power of the spot module is 10W. The average thermal resistance between the die junctions and the housing is 2 K/W. The optical efficiency of the module is 70%. The maximum luminous flux in the beam, which has a full width at half maximum (FWHM) of 20-25°, is about 200 lm. The system has thermal and optical sensors that provide the signals for a closed control loop to compensate for run-up and differential ageing effects. The resulting color point accuracy in the u'v' color space is better than 0.01. This shows the feasibility of easy-to-use lighting modules that offer advanced lighting options with adjustable, reliable and accurate output.
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