UNIQUE HUE SHIFTS UNDER DIFFERENT LIGHT SOURCES

The choice of which colours are more suitable to measure the colour rendering properties of a light source is rather controversial. Unique hues seem particularly suitable because all colours we can perceive show a larger or smaller similarity to only the four unique hues + white and black. We studied the changes that three series of unique hues (Yellow Red Blue Green) show when observed under six different light sources. First of all results show that under the fluorescent CCT 6500 K all three nuances of the unique red are chosen slightly, but significantly, shifted towards the yellowish interval in the NCS (Y95R on average). Secondly results show that the unique red undergoes greater deviations under different illuminations, mostly when it is highly chromatic. Under LED sources also unique yellow and green show some significant deviations. The procedure seems very useful to elaborate a new colour rendering index.