A new color control system is described and implemented for a five-color LED light engine, covering a wide white gamut. The system combines a new way of using pre–calibrated lookup tables and a rule-based optimization of chromaticity distance from the Planckian locus with a calibrated color sensor. The color sensor monitors the chromaticity of the mixed light providing the correction factor for the current driver by using the generated lookup table. The long term stability and accuracy of the system will be experimentally investigated with target tolerance within a circle radius of 0.0013 in the uniform chromaticity diagram (CIE1976).
The rapid development in flux and efficiency of Light Emitting Diodes (LED) has resulted in a flooding of the lighting market with Solid State Lighting (SSL) products. Many traditional light sources can advantageously be replaced by SSL products. There are, however, large variations in the quality of these products, and some are not better than the ones they are supposed to replace. A lack of quality demands and standards makes it difficult for consumers to get an overview of the SSL products. Here the results of a two year study investigating SSL products on the Danish market are presented. Focus has been on SSL products for replacement of incandescent lamps and halogen spotlights. The warm white light and good color rendering properties of these traditional light sources are a must for lighting in Denmark and the Nordic countries. 266 SSL replacement lamps have been tested for efficiency and light quality with respect to correlated color temperature and color rendering properties. This shows a trade-off between high color rendering warm white light and energy efficiency. The lumen and color maintenance over time has been investigated and results for products running over 11000 h will be presented. A new internet based SSL product selection tool will be shown. Here the products can be compared on efficiency, light quality parameters, thus providing a better basis for the selection of SSL products for consumers.
Museum lighting present challenges due to the demand for a high color rendering index (CRI), color uniformity
and the damaging effects of both visible and invisible radiation. Golden objects are furthermore normally
displayed with illumination which has a correlated color temperature (CCT) of 2200 K, a CCT that is not
commercially available from single LEDs. An LED system that conforms with these requirements has been
developed and implemented at The Royal Danish Collection at Rosenborg Castle. Color mixing of commercial
LEDs (red, cyan, and white) was employed to achieve the spectral power distribution needed for the CCT and
a CRI above 90, for all CRI test color samples. Replacing the traditional low voltage incandescent lighting has
shown energy saving above 70 %. Harmful IR radiation was reduced by 99 %. Temperature fluctuations in the
display cases were reduced from several degrees Celsius to below one, despite the fact that the lighting units
were placed within the display case. Spatial color uniformity of the illumination and uniformly colored shadows
was achieved by use of a highly diffusing reflector dish which avoids direct illumination from the LEDs.
Given the problem of metamerisms inherent in color mixing in light-emitting diode (LED) systems with more
than three distinct colors, a method for optimizing the spectral output of multicolor LED system with regards to
standardized light quality parameters has been developed. The composite spectral power distribution from the
LEDs are simulated using spectral radiometric measurements of single commercially available LEDs for varying
input power, to account for the efficiency droop and other non-linear effects in electrical power vs. light output.
The method uses electrical input powers as input parameters in a randomized steepest decent optimization.
The resulting spectral power distributions are evaluated with regard to the light quality using the standard
characteristics: CIE color rendering index, correlated color temperature and chromaticity distance. The results
indicate Pareto optimal boundaries for each system, mapping the capabilities of the simulated lighting systems
with regard to the light quality characteristics.