A Methodology for Perceptual Metrics in Lighting Design and Ambiance Experience

Introduction

This paper presents a study conducted in 2022-23 within a real-world environment, introducing a novel approach for assessing perceived light quality and experienced ambiance. The methodology incorporates typologies of lighting principles and contrast ranges of interior colours, along with a collection of descriptive terms for the character of light, shadow, and ambiance. Traditional methods for measuring light quality rely on physical measurements of light radiation, providing data on stimuli but lacking insights into the experienced quality. However, the experience of a room's atmosphere significantly impacts both well-being and health, with the character of light and colour schemes being key factors in creating ambiance (1,2). This new method has the potential to complement physical measurements by defining light quality in experiential terms, thereby enhancing communication, conceptualization, and evaluation of lighting environments in both practical applications and research. The method has been developed and tested in repeated studies in controlled environment using scale models. The results suggest that the method is useful for evaluations in real environments, since they are comparable with the results from previous studies with scale models, and in workshops with researchers and practitioners in the lighting industry.

Method

The study is part of an interdisciplinary research project focused on the experienced qualities of light, ongoing since 2016 (1,2,3). Various methods have been developed within this project, originating partly in sensory analysis and behavioural science, and partly in lighting design practice and perception research. A basis for the development of the method used in this study is the understanding that the light we perceive is mostly reflected, meaning the properties of reflective surfaces are equally significant for the spatial experience as the light distribution. Another crucial component is that visual stimuli and image formation, as well as spatial perception, depend more on contrast than on light level. Consequently, the typologies and the method are designed to capture perceived contrast as much as perceived light level.

In the study, two large study rooms at a university, with almost identical proportions and dimensions but very different lighting and colouring, were evaluated by 20 subjects. They used a questionnaire with unipolar scales for light character, shadow character, and ambiance. The subjects were also asked to assess the perceived light level, contrast, and their preferences. One room was quite dark, with subdued colours and lighting consisting of spotlights and task lights creating higher contrast levels. In contrast, the other room had bright walls and lighting exclusively from ceiling-mounted fluorescent fixtures, providing even light. The light levels and spectra in both spaces were measured, along with the colours of walls and furnishings using NCS Indexes and colour scanners. The outcome was compared with the results from a previous study, including 25 subjects in a controlled environment using 14 scale models with different lighting design and colour schemes. 

Results

A statistical analysis showing mean values indicates that the results from the real-world study coincide with those from two specific scale models. The words used to describe the light, shadows, and ambiance are almost the same, although more words are used to describe the more complex and elaborate real rooms. The outcomes from both studies also indicate that moderate contrast, created by light distribution, shadows, and/or the colour scheme, is a crucial factor for creating both visual quality and an appealing ambiance. In both cases, the preferred rooms were those using directed lighting and a varied colour scheme.

Conclusion

The results provide a strong indication and a validation of the method being useful for assessing perceived light quality in real environments. Detta öppnar möjliheter för användning av den både inom bryggprocessen där rekommenderade ljusnivåer ofta ses som en kvalitesgaranti för goda ljusmiljöer, men även inom forskning där den till exempel kan användas i kombination med psykologiska studier av ljusmiljöer.

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