A STUDY ON THE EVALUATION METHOD OF COLOUR RENDERING PROPERTIES OF MUSEUM LIGHTING AT LOW ILLUMINANCE

摘要

The purpose of this study is to clarify colour rendering properties at low illuminance and also to try to develope the new calculating method to evaluate the colour rendering values taking into consideration of illuminance. The subjective experiment on colour appearance of the two-colour combinations (the set of the pairs of two colour chips) and the mosaic colour samples (mosaic colours) illuminated by the test and the reference light sources with different illuminance was carried out. The result showed that the subjective evaluation of colourfulness, brightness, and preference under the LED white light source(Ra19) composed of R/G/B LED chips at 700 lx and 10 lx was higher than those under the other light sources (the fluorescent lamp with Ra96, the LED lamp of blue LED and yellow phosphor with Ra82, the warm-white fluorescent lamp with Ra60). It was suggested that the current CIE Ra or Ri would not be sufficient when colour rendering properties of narrow band mixed-LEDs were evaluated especially at low illuminace level. To examine whether the current CRI are appropriate or not for subjective evaluation of colour appearance at very low illuminance, we tried to verify the several calculation methods of the colour rendering values taking into consideration of illuminance. As the result, it was shown that the colour rendering properties of LED lighting at very low illuminance level could be evaluated by the Gamut Ratio (GR) or the Feeling of Contrast (FCI).