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.

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