Editorial: The meaning of preference
Anyone who has seen the item of correspondence in the last issue of Lighting Research and Technology will be aware that an argument has broken out in the field of light source spectrum optimization. The argument is about the status of studies of preferred light spectra. The authors of the correspondence argue that colour preference is a misleading concept with no scientific validity. Unlike colour fidelity, it is not objective, nor is it based on colour science. Rather, colour preference is subjective and unstable. It will change in different situations and over time depending on the presence or absence of different surface colours, the culture of the observers, the context in which the lighting is seen and the vagaries of fashion. While argument may rage over how 'scientific' measurements of colour preference are there can be little doubt that peoples' preferences do matter commercially. Anyone who has tried to sell a product knows that it is much easy to do so if the product matches peoples' preferences than if it does not. I remember attending a lecture in which the speaker expounded the virtues of a teapot designed on scientific principles so that turbulent flow was eliminated as were dribbles. Unfortunately, he also confessed that it had proved impossible to get the design accepted by the public because the teapot looked like a bedpan. Given that preference for a light source spectrum matters, is it a legitimate subject of study, and how should such studies be evaluated? Given the ability of solid state lighting to produce almost any spectrum, attempting to answer questions such as what light spectrum is most preferred, when and where and by whom is obviously legitimate although the results may not add much to scientific understanding. As for how such studies should be evaluated, in addition to the usual matters of experimental design and statistical analysis, this comes down to identifying the relevance of the conditions examined for any proposed application. For assessing relevance, it is always necessary to know the assumed context and the number and culture of the observers. Three other aspects that should be considered are the nature and number of surface colours included in the scene, the time for which the observer was exposed to the light spectrum and the size of the visual field over which the light spectrum appears. The hues and saturations of the surface colours present matter because preference is likely to be affected by how well the surface colours present are rendered by the light spectrum. Time of exposure is important because colour adaptation may alter the strength of the preference. Visual field size may be significant because preference may be different when the observer is immersed in the light spectrum rather than looking at a display on a screen. It is only by considering such questions that the relevance of a specific study to a proposed application can be determined.