Psychological Processes Influencing Lighting Quality

Veitch and Newsham proposed a behaviorally-based model for lighting quality research, in which individually-based processes mediate the relationships between luminous conditions and such behavioral outcomes as task performance, mood, social behavior, aesthetic judgements and satisfaction. This review paper summarizes the state of knowledge concerning mediating psychological processes: perceived control, attention, environmental appraisal, and affect. These processes were selected because of their relevance to the explanations often given for lighting design choices. More explicit use of theoretically-driven predictions to guide lighting research would result in greater precision in our comprehension of lighting-behavior relationships to form the foundation of empirically-based lighting recommended practice. Psychology and Lighting Quality / 2 Introduction Surveys of office employees consistently report that lighting is among the more important features of office design and furnishings. Likewise, in the professional community of lighting designers and illuminating engineers, there is a long history of speculation that the quality of the luminous environment can influence task performance, comfort, and well-being, effects that are fundamentally psychological -that is, behavioral, in nature. This paper reviews the relevant literature concerning such effects, in an attempt to provide direction for lighting recommended practice and to further lighting quality research. Stein, Reynolds, and McGuinness once defined lighting quality as "a term used to describe all of the factors in a lighting installation not directly connected with quantity of illumination. p.887) Their definition, although flexible enough to be applied to a wide variety of lit environments, offers little guidance concerning how to measure the quality of a lit environment. Veitch and Newsham proposed that lighting quality exists when the luminous conditions support the behavioral needs of individuals in the lit space. This definition has the merit of being measurable, but it only considers the immediate consequences of the luminous conditions on the individuals. More accurately, this definition should be expanded to include architectural and economic considerations, as well as individual well-being (Figure 1). The quality of the lighting in any given installation is determined in the balance of these (sometimes conflicting) dimensions. One central concern for the lighting community is the means by which we describe the luminous conditions in a space. Guidelines for lighting practice, for example, use photometric criteria to describe the minimum conditions required for good lighting practice (which, one hopes, will also achieve good lighting quality). There is general agreement that luminance, luminance distribution, uniformity, flicker rate, and spectral power distribution describe most of these quantities. Lighting system characteristics such as individual control, indirect lighting, and the use of daylight are also thought to contribute to good-quality lighting. Generally speaking, lighting practitioners strive to create luminous conditions that will optimize outcomes for individuals, but often with the intent of optimizing organizational outcomes such as retail sales and the clients bottom-line. These luminous conditions, like other environmental conditions, have effects on people that differ depending on individual characteristics such as age and sensitivity, and they may do so through any of several mechanisms (Figure 2). The mechanisms are theoretical constructs, useful to many scientific disciplines because of their utility for organizing empirical evidence and inductive reasoning into explanatory systems. For convenience, these parallel processes can be divided into two broad categories: psychological processes, which are the focus of this paper, and psychobiological processes such as visibility, photobiology, and arousal. The knowledge of these specific mechanisms that will arise from research will enable precise predictions about expected outcomes, predictions drawn from lighting research and from other topic areas that investigate the same processes. The manner of presentation in Figure 2 is deliberate, in that the lighting conditions are concurrent, the individual and group processes occur simultaneously, and the outcomes occur concurrently. For any individual at any one time, behavior is influenced by many causes. In the review, the sections devoted to each process are structured by the luminous conditions addressed in the body of research identified in our literature search. The focus of this paper is on the scientific evidence concerning the intervening psychological mechanisms that produce behavioral effects in response to luminous conditions (an earlier attempt is given in Veitch and Newsham). The goal is to describe the state of knowledge about these effects both to serve as initial input to revised recommended practice documents based on the lighting quality framework, and to guide future research. Others, with experience in lighting design, daylighting, luminaire design, and energy use, are better positioned to contribute to the discussion of the other influences on lighting quality diagrammed in Figure 1. (For instance, Loe and Rowlands have opened the discussion on the broader design end energy issues related to achieving good-quality lighting.) This review is organized in terms of the intervening psychological processes that are believed to underlie the lighting-behavior relationship: perceived control, attention, environmental appraisal, and affect. This is not an exhaustive list of possible mechanisms, but a categorization of the principal ones currently in use. This set was chosen because of the frequency with which these mechanisms are invoked as explanations of lighting design choices. When we understand why certain luminous conditions produce the behavioral outcomes we desire, then we will be able to re-create those conditions, and those outcomes, more reliably. Within the section for each of the four psychological processes are subsections discussing the operation of that process in response to various luminous conditions: luminance/illuminance; uniformity across tasks; luminance distributions within rooms; glare; spectral power distribution; flicker; indirect lighting systems; and, windows and Psychology and Lighting Quality / 3 daylighting. These categories generally agree with the luminous conditions described in various recommended practice documents. Not every possible luminous condition has been studied in relation to each process, so the number of subsections varies for each psychological process (indeed, in the section on perceived control it was impossible to distinguish between studies on the basis of luminous conditions). Poor-quality research is a major impediment to understanding. Such criticism of lighting research is longstanding, recognizing its weaknesses in scientific procedure and statistical analysis. Nonetheless, the existing body of writing about lighting has formed the basis for lighting education and recommended practice documents, Therefore, the review is inclusive, including empirical work from many sources that might be familiar to readers. A detailed critique of each article is beyond the scope of this paper. Instead, major limitations are noted where appropriate, and those conclusions are drawn that were judged supportable from the data provided. Economic considerations have driven much lighting research, with the result that the vast majority of investigations have considered lighting for offices, with relatively few investigations occurring in other settings. Accordingly, this review focuses on office lighting applications, although studies from other settings are included where their results are relevant. This review is limited to suprathreshold viewing conditions at adaptation levels typical of interiors. Psychological processes in lighting-behavior relationships Perceived Control Among the classic observations in modern psychology is the finding that perceived control can moderate stress reactions. Glass and Singer found that when people were given the opportunity to end an aversive noise (although they did not use it), they did not experience the negative aftereffects on task performance that were observed in people who had not had the opportunity. When control over aversive stimuli is not available, learned helplessness can result, in which individuals suffer emotional, cognitive, and behavioral deficits. Furthermore, belief that the absence of control leads to feelings of unhappiness and powerlessness is widespread. This belief is often used to justify the adoption of individual lighting controls, although few empirical investigations exist to justify this additional expense. Field surveys are consistent in reporting that a sizable percentage of office employees prefer to have some degree of control over their office lighting. Fifty-four per cent reported this in a large North American survey, and 67% in one Midwestern US building. Lighting designers apparently believe that providing individualized lighting controls has far-reaching benefits for occupants. However, perceived control does not always lead to desirable outcomes. Burger observed that people will decline control when it carries the risk of not achieving a desired goal or if it creates uncomfortable concern with self-presentation. If an expert seems more likely to make the correct choice, or if one risks looking foolish by making the wrong choice, this will be a choice that one does not want. Wineman concurred that in certain situations, control can lead to undesired effects if it requires choices one did not wish to make. One experiment to date concerning the performance effects of perceived control over lighting obtained results consistent with this pattern. The experiment varied the degree of control available for wor