PNNL

Abstract

After decades of debate, new methods for characterizing color rendition have been formalized, providing an improved system of tools to aid technology developers and lighting specifiers. Solid-state lighting, previously burdened by legacy measures based on outdated science, is positioned to take advantage of these new tools to provide tailored, efficient lighting that better meets the needs of specific architectural lighting applications. This transition requires new guidance, however, presenting an opportunity for researchers. There are several key methodological considerations specific to experiments investigating color rendition that will help build a base of guidance that can be widely applied. The importance of these ideas mostly stems from new knowledge gained in the last five years, but their origins date back much further. 1.The spectral power distribution must be adequately varied to stress the measure(s) of color rendition being evaluated. Often, this means varying the gamut shape—the pattern of shift across different hues—to probe weaknesses of hue-averaged characterizations, avoiding misleading conclusions resulting from limited variation in the stimuli. 2.Evaluating the role of chromaticity on color quality evaluations requires careful accommodation of chromatic adaptation to prevent a centering bias. Asking for delayed responses may be insufficient if chromaticity changes are apparent to participants, just as side-by-side viewing of different chromaticities may not produce results that can be reliably applied in the field. It is also critical that color rendition and chromaticity conditions are varied independently. 3.The stimulus being viewed is the interaction of light and objects’ spectral reflectances. This interaction should be quantified in order to assess how derived guidelines will apply measures using standardized color sample sets. Although light source characterizations are typically used to model responses, the objects and their presentation may strongly influence evaluations. 4.Context is important. Many factors—some investigated, others hypothesized—can influence subjective evaluations of color quality, including illuminance level, type of scene, object familiarity, color composition, viewing duration, and viewer traits. Although their influence on research results is unavoidable, the effects of these contextual factors must be carefully considered in developing guidance. Appropriate experimental design can often mitigate negative consequences arising from these considerations. At a minimum, it is crucial to understand how each of these considerations can influence experimental outcomes, as well as the interpretation and application of the results in practice. Consulting other experts prior to conducting an experiment can help ensure appropriate, up-to-date research methods will be used, so that the results will be novel and useful—and not rejected during peer review. There is an interesting feedback loop: technology development provides new research tools, which allow for refined research methods and new results that lead to more technology development. It is time to make a concerted, collective effort to improve color rendition research so that the full potential of solid-state lighting and new characterization methods can be realized, ensuring that high-efficiency, high-utility, high-appeal lighting systems become standard.