Road lighting: A pilot study investigating improvement of visual performance using light sources with a larger gamut area

Many past studies investigating visual performance focused mainly on the effect of luminance contrast between the target and background. Other studies have suggested the importance of colour contrast on visual performance. This pilot study was designed to investigate whether visual performance in the context of road lighting can be improved by enhancing the chroma of targets. Observers were asked to detect an off-axis target with different levels of luminance, hue, and chroma on a uniform background at 1.5 cd/m2. When the target and the background were set to the same luminance, a zero luminance contrast, the detection rates were significantly lower and the reaction times were significantly longer. Enhancing the colour contrast between the target and the background by increasing the target chroma level, however, was found to improve visual performance to similar levels as those when the target was revealed by luminance contrast against the background. Such an enhancement on colour contrast can be achieved in practice using light sources with a greater colour gamut size.

Colour gamut size and shape influence colour preference

Two psychophysical experiments were conducted to investigate the effect of colour gamut size and shape on colour preference. In the first, two side-by-side booths were designed to resemble a retail setting with clothing; in the second, a single booth was designed to resemble a restaurant setting, but also included a mirror to permit the observer's evaluation of skin tone. These settings were illuminated with two sets of sources, where, compared to a fixed reference, one set created modest chroma enhancement and the other set created greater increases in object chroma. Within each set, gamut shape varied, meaning different hues were saturated, even though, on average, the spectra created the same average increase in chroma. When objects were unfamiliar, as with the fabrics, all chroma-enhancing spectra were preferred to the fixed reference regardless of the gamut shapes. When familiar objects were present, such as food, observers were more discerning about changes in chroma and hue. We conclude that a graphic of gamut shape is an important adjunct to average measures of colour fidelity and gamut.