Marc Fontoynont

Assessing the colour quality of LED sources: Naturalness, attractiveness, colourfulness and colour difference

The CIE General Colour Rendering Index is currently the criterion used to describe and measure the colour-rendering properties of light sources. But over the past years, there has been increasing evidence of its limitations particularly its ability to predict the perceived colour quality of light sources and especially some LEDs. In this paper, several aspects of perceived colour quality are investigated using a side-by-side paired comparison method, and the following criteria: naturalness of fruits and vegetables, colourfulness of the Macbeth Color Checker chart, visual appreciation (attractiveness/ preference) and colour difference estimations for both visual scenes. Forty-five observers with normal colour vision evaluated nine light sources at 3000 K, and 36 observers evaluated eight light sources at 4000 K. Our results indicate that perceived colour differences are better dealt by the CIECAM02 Uniform Colour Space. Naturalness is better described by fidelity indices even if they did not give perfect predictions for all differences between LED light sources. Colourfulness is well described by gamut-based indices and attractiveness was found to correlate best with gamut-based indices but also with a preference index or a memory index calculated without blue and purple hues. A very low correlation was found between appreciation and naturalness indicating that colour quality needs more than one metric to describe subjective aspects.

Consideration of daylight’s colour

Abstract The aim of the study is to underline the contribution of colour in daylighting projects as an objective parameter of visual performance and pleasantness. Window technology offers ways to use daylight in buildings. Glazing, shading systems and indoor materials modify its aspect by offering a large variation of its colour. However, colour of daylight changes greatly according to climate, spatially and temporally. Variation of the colour of daylight is illustrated as well as an example of the resulting change of surface colours with or without a type glazing. Then, a method to predict directional colour of skylight is suggested with the intention to apply it in daylighting calculations.

Preferred Color Rendition of Skin under LED Sources

ABSTRACT A psychophysical experiment was conducted to investigate the perceived color rendition of facial complexion under different spectral power distributions (SPDs). Sixty-three subjects completed a categorical evaluation of their own skin under 20 light sources at 2700 K (fluorescent and LED), in a full-size booth. The aim was to investigate the influence of SPD on the appreciation of observers of their own complexion. Three different types of skins were evaluated and statistical analyses showed that there were significant differences between some SPDs. Correlations between subjective estimation and color metrics were investigated to find which metrics best describes visual preference.