This study investigates colour harmony in visual experiments in order to develop a new quantitative colour harmony model. On the basis of new experimental results, colour harmony formulae were developed to predict colour harmony from the CIECAM02 hue, chroma, and lightness correlates of the members of two-or three-colour combinations. In the experiments, observers were presented twoand three-colour combinations displayed on a well-characterized CRT monitor in a dark room. Colour harmony was estimated visually on an 11 category scale from 25 (meaning completely disharmonious) to þ5 (meaning completely harmonious), including 0 as the neutral colour harmony impression. From these results, mathematical models of colour harmony were developed. The visual results were also compared with classical colour harmony theories. Two supplementary experiments were also carried out: one of them tested the main principles of colour harmony with real Munsell colour chips, and another one compared the visual rating of the new models with existing colour harmony theories.
In Part I of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0-100) labelled by semantic categories (e.g. 'moderate', 'good' and 'very good') in the context of office lighting. Five customary light sources without object saturation effect illuminated a table with coloured objects in a real room. The observers' assessments were predicted by recent colour quality indices and selected pairs of indices combined linearly. Criterion values of the indices for 'good' colour preference and vividness were determined to provide a usable acceptance limit for the spectral design and evaluation of light sources. To predict colour preference, correlated colour temperature turned out to be useful. In Part 2 of this work, another experiment with the same method but using multi-LED spectra with more object saturation will be analysed and the two datasets will be merged.
The authors represent a research consortium 1 which has adopted a task performance based approach for nighttime driving to establish a system for photometry in the mesopic region. This article analyses the experimental investigations described in earlier articles on visual performance in the mesopic domain using reaction time, detection threshold, and discrimination threshold techniques. These results are used to develop a system for mesopic photometry, which balances the quality of the fit to the experimental data with the ease of practical implementation by the lighting industry. A more complex model is also described, which takes account of the chromatic visual response channels and thus provides a better fit to some of the experimental results (particularly those involving monochromatic stimuli), but describes the totality of the data less well and is furthermore less suitable for practical photometric measurements.
In Part 2 of this work, observers scaled colour preference, naturalness and vividness visually on interval scales (0–100) labelled by semantic categories (e.g. ‘moderate’, ‘good’ and ‘very good’) in the context of food lighting using the same questionnaire as in Part 1. Seven multi-LED light sources with more or less object saturation effect illuminated a viewing booth with coloured food objects. The two datasets (Part 1: room + Part 2: viewing booth) were merged and the observers’ assessments were predicted by recent colour quality indices and CIELAB chroma differences. Linear combinations of selected pairs or triads of descriptors were used to predict the merged dataset. Criterion values to achieve ‘good’ preference, naturalness and vividness level were determined.
Numerous efforts have been made to investigate how to characterize the effect of light sources on colour preference. This paper describes a psychophysical experiment to compare the colour preference evaluation among three sources for different lighting applications. Three lighting applications – restaurant, retail display, and supermarket – were created in two side-by-side full-scaled rooms. It was found that the colour preference varied with the lighting applications. Although none of the existing single-value measures can predict the preference for all three applications, a single measure is necessary for general consumer use given a careful definition of general lighting. In addition, lighting application specific measures could be useful for lighting professionals and experts. To provide detailed information, a colour distortion icon, with improved test colour samples will be useful.
Light source colour quality is a complex phenomenon with several visual and cognitive components. Subjective colour preference, naturalness and vividness assessments of reddish cosmetic products in a viewing booth lit by light sources with a correlated colour temperature of 3200 K and to 550 lx were analysed and modelled by a new combined colour quality formula – a linear combination of a colour fidelity index and a measure of chroma change. Results of the warm white light sources described in all three parts of this work were merged. They were modelled by optimising the parameters of the same formula. The formula supports multi-LED light sources with moderately accentuated local spectral maxima to enhance object chroma over a moderate range.
The preference for the chromaticity of high illuminance, high colour rendering LED illumination of different scenes was investigated for Chinese and European observers. An experiment about the preference for perceived illumination chromaticity was conducted with the same multi-LED light engine, same viewing booth and same coloured objects transported between Germany and China. Observer preference for perceived illumination chromaticity was significantly influenced by correlated colour temperature (2700 K–6500 K), object scene colour (red, blue or mixed), cultural background (Chinese or European origin, living in Germany or in China) and gender (men, women). The results can be used to choose an appropriate correlated colour temperature (e.g. warm white or cool white) for a high-quality lighting product to illuminate different object scenes (e.g. red or blue objects) so as to achieve good user acceptance in the global market.
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