The aim of the experiment was to evaluate paired comparison subjective assessments of a range of artworks illuminated alternately by a tungsten halogen MR spotlight and by an experimental 3-band source, both having the same correlated color temperature.
It was predictable that the CCT and the color appearance of an MR lamp could be matched by a 3-band source that would have significantly higher radiant luminous efficacy than the MR lamp. It was expected that if subjects were presented with an achromatic scene alternately lit to the same illuminance by these two types of light source, they would not differentiate between them. What could not be predicted was how they would respond to a scene that involved colored materials.
The basis for the comparison was an illuminance of 50 lux on the art work provided by an MR spotlight, as this the type of lighting and light level are widely adopted for display of susceptible exhibits. However, the CCT of the MR lamp is low: 3000 K at full voltage, and in practice often lower due to being dimmed to provide 50 lux. It was decided that the experiment should also include an intermediate color temperature source, and this was achieved by repeating the procedure using a new type of MR lamp that has a CCT of 4700 K at full voltage.