Kees Teunissen

How is museum lighting selected? An insight into current practice in UK museums

The results of a series of interviews with museum professionals on the subject of museum lighting specification and selection are reported, with the aim that this report should provide an insight into current practice. Specific attention is given to the usage of industry parameters (lux, CIE-Ra, CCT), and to investigating the level of ubiquity of light-emitting diode (LED) technology. It is found that the damage potential of lighting is considered most commonly in terms of lux dosage, that a minimum cut off in terms of CIE-Ra is used to specify lighting ‘quality’, and that LED usage is growing, primarily as a result of institution-wide energy use reduction drives.

Progress in characterizing the multidimensional color quality properties of white LED light sources

With the introduction of solid state light sources, the variety in emission spectra is almost unlimited. However, the set of standardized parameters to characterize a white LED light source, such as correlated color temperature (CCT) and CIE general color rendering index (Ra), is known to be limited and insufficient for describing perceived differences between light sources. Several characterization methods have been proposed over the past decades, but their contribution to perceived color quality has not always been validated. To gain more insight in the relevant characteristics of the emission spectra for specific applications, we have conducted a perception experiment to rate the attractiveness of three sets of objects, including fresh food, packaging materials and skin tones. The objects were illuminated with seven different combinations of Red, Green, Blue, Amber and White LEDs, all with the same CCT and illumination level, but with differences in Ra and color saturation. The results show that, in general, object attractiveness does not correlate well with Ra, but shows a positive correlation with saturation increase for two out of three applications. There is no clear relation between saturation and skin tone attractiveness, partly due to differences in preference between males and females. A relative gamut area index (Ga) represents the average change in saturation and a complementary color vector graphic shows the direction and magnitude of chromatic differences for the eight CIE-1974 test-color samples. Together with the CIE general color rendering index (Ra) they provide useful information for designing and optimizing application specific emission spectra.