Museum lighting for golden artifacts, with low correlated color temperature, high color uniformity and high color rendering index, using diffusing color mixing of red, cyan, and white-light-emitting diodes

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.