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Lighting guidelines from lighting quality research
Veitch, J. A.
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Lighting guidelines from lighting quality research
J.A. Veitch BSc BA(Hons) MA Ph.D
National Research Council of Canada / Institute for Research in Construction Bldg M-24, Montreal Road Campus. Ottawa, ON K1A 0R6 Canada
tel. +1 613 993 9671 / fax +1 613 954 3733 / e-mail
Jennifer.Veitch@nrc.ca
Summary
To judge the quality of a lighting installation is to determine how well it meets context-specific goals in the areas of architecture, economics, and individual well-being. The goals for individual well-being are behaviours such as task performance, mood, social behaviour, aesthetic judgements and satisfaction, that occur as a result of internal processes influenced by luminous conditions. These processes fall into two categories, psychobiological processes (visibility; photobiology; and, stress and arousal), and psychological processes (attention and environmental appraisal; perceived control; and, affect [emotion] and expectations). Empirical and theoretical work from a variety of scientific disciplines adds to our understanding of how lighting influences human experience and behaviour by acting on these processes. Some of these, such as visibility, are well-understood and obviously relevant to lighting practice. Others, such as photobiology, are in their infancy, but have the potential to substantially change lighting practice. These internal processes can provide a valuable organising principle for the translation of research findings into lighting practice.
Résumé
Juger de la qualité d’une installation d’éclairage, c’est déterminer de quelle manière elle permet d’atteindre des buts propres à certains contextes sur les plans architectural, économique et du bien-être individuel. En ce qui concerne ce dernier, les buts sont par exemple la performance professionnelle, l’humeur, le comportement social, les jugements esthétiques et la satisfaction, qui résultent de processus internes influencés par les conditions lumineuses. Ces processus se rangent dans deux catégories : psychobiologique (visibilité, photobiologie, stress et éveil) et psychologique (attention et évaluation de l’environnement, contrôle perçu, affect [émotion] et attentes). Les travaux empiriques ou théoriques accomplis dans diverses disciplines scientifiques aident à prendre conscience que l’éclairage influe sur le vécu et le comportement des personnes en agissant sur ces processus. Certains de ces processus, par exemple la visibilité, sont bien compris et manifestement utiles pour déterminer les façons de faire en matière d’éclairage. D’autres, comme la photobiologie, en sont encore à leurs débuts mais ils pourraient modifier considérablement ces façons de faire. Ces processus internes peuvent constituer un important principe d’organisation en vue de la traduction des conclusions des recherches en pratiques d’éclairage.
1.0 Introduction
Lighting quality is now firmly established as the fundamental goal of lighting design. No longer concerned with visibility alone, the degree of excellence attained by a lighting installation is now defined as a relative judgement depending on the context in which the project occurs, and including the components of individual well-being, architecture, and economics (Figure 1) [1]. The context will determine the relative importance of the three components and of elements within those components. For instance, the lighting in a surgical suite will achieve good lighting quality only when visibility of two- and three-dimensional objects is excellent in terms of both luminance and colour contrast. The cost of the lighting to achieve that goal will be relatively unimportant. On the other hand, the lighting in a living room will require less attention to visibility of very fine details and more attention to lighting for social interactions. The cost of the lighting will be more important to some homeowners than to others.
Figure 1. Lighting quality: the integration of individual well-being, architecture, and economics.
Understanding the variables that influence the goals of a lighting installation is among the next tasks for lighting researchers [1]. One can divide the broad domain of lighting research into three overlapping subfields, all of which have roles to play in the establishment of technologies, design processes, and knowledge pertaining to improving lighting quality. These are: research aimed at developing lighting (and daylighting) technologies; architectural and design research; and, human factors research (encompassing biological and psychological processes and effects). This paper concerns the development of guidelines for lighting quality from research in the third area: How can we move from raw information about lighting effects on individual well-being to useful application of that information?
Considerable effort has been expended, without a generally-agreed-upon comprehensive definition of lighting quality, to elucidate the relationships between luminous conditions and specific behavioural outcomes such as visibility, task performance, and preference. Our achievements in this domain have as yet been modest in comparison to the effort expended [2,3].
Commentators have pointed out that one reason for this limited progress is the absence of a theoretical basis for most lighting research that concerns the effects of light and lighting on people [3,4]. The researchers rarely have framed their research questions in terms of the organising power of empirical observation married to inductive reasoning. There has generally been no basis for the choice of particular outcome measures, and no reason to expect certain outcomes.
Lighting researchers share an interest in these outcomes with most behavioural scientists, which makes it possible to borrow from the behavioural sciences, psychology in particular, in order to make predictions about the effects of luminous conditions. A general model for this type of theoretical model is shown in Figure 2. The principal interest for most lighting research is marked by a path with thick arrows from luminous conditions, through internal processes in the individual, to the behaviours exhibited by the individual. Other variables that can influence these processes are also included and may from time to time be the focus of lighting research. Organisational outcomes are illustrated as the product of individual and group outcomes, and other (unnamed) factors. Despite their indirect link to lighting conditions, the organisational outcomes are not trivial because of the pressure to find economic justifications for improved lighting quality.
Figure 2. Conceptual model showing relationships between lighting conditions, internal
conditions and processes, and individual, group, and organisational outcomes. The grey box encloses variables and processes internal to individuals.
The internal processes that mediate the lighting-behaviour relationship offer organising principles for the attempt to summarise current knowledge and to direct future efforts. Two comprehensive reviews of the literature (currently in press) have used this approach to integrate findings from a diverse literature [5,6]. In all domains, the scope for innovative research is great. However, little effort has occurred towards using these organising principles to derive practical guidelines that would be of use in making choices about a lighting installation. This is the focus here.
2.0 Research-based Guidelines for Quality Lighting
This paper builds on earlier literature reviews, starting from the conclusions drawn from scientific publications relating to six internal processes: visibility; photobiology; stress and arousal; attention and appraisal; affect, expectations, and beliefs; and, perceived control.[5,6]. The reviews concluded that except for visibility, the level of understanding of all of the processes is low, which will make these guidelines preliminary and open to revision and addition. However, in all cases the existing literature can direct the lighting design process to include considerations that might otherwise have been overlooked. Table 1 provides a start at research-based lighting guidelines framed in terms of internal psychobiological and psychological processes. The transition from general guidelines such as these to specific guidelines with target photometric values for various conditions will require extensive research effort.
2.1 Visibility
Our knowledge is greatest in this area. To optimise visibility, tailor the illuminance on the task to the task and viewer demands. Alternatively, one could consider changing the task demands to avoid the need for increasing illuminance. This approach uses less energy and is less costly to the client. Best outcomes for visibility also avoid contrast reduction from veiling luminances or intraocularly from direct glare. Reasonably accurate models to predict these outcomes exist already [7].
2.2 Photobiology
The fundamental science in this area is new, but effective applications of this knowledge exist, particularly for adjusting sleep-wake cycles for people working shifts [6]. Among the most dramatic examples (because of the consequences of fatigue-induced errors) of the successful application of these lighting strategies is NASA's use of this technology to shift the circadian rhythms of employees during shuttle missions [8]. Special installations tailored to the specific needs of the task, setting, and shift are needed to use this knowledge effectively, and the workers themselves must comply with the protocol by avoiding light exposure during scheduled dark periods.
2.3 Arousal and stress
The fact that light exposure causes wakefulness, which underlies the photobiology applications above, probably accounts for much of the popularity of arousal as an explanatory mechanism for lighting effects on behavior. However, the literature regarding the effects of increasing illuminance during daytime exposures provides only weak support for the hypothesis that increasing illuminance increases generalized arousal [6]. The well-known findings of the Hawthorne studies [9] are valid in that relationships between illumination and work are rarely simple [e.g., Ref. 10].
However, lighting conditions can create stressful physiological responses, increasing arousal in the classical 'fight or flight' sense. Glare, whether from a direct source or a reflected luminaire, is the most obvious of these (this underlies certain interrogators' use of a bright light shining in the eyes of prisoners to motivate answers). Low-frequency flicker (in the range of approximately 60-200 Hz, estimated based on current knowledge) can also serve as a stressor, particularly (it seems) for younger people [11].
Table 1. Preliminary Lighting Guidelines for Workplaces
Mediating Process Guidelines Comment
Visibility (Section 2.1)
• appropriate horizontal & vertical illuminances for tasks and viewers
• consider changing task demands • control unwanted light (glare),
both direct and reflected
• orientation of working area & luminaires an issue
• use high--frequency ballasts for fluorescent lights
• young people might be more sensitive to flicker
Photobiology (Section 2.2)
• scheduled light exposure for shift work adjustment (possibly also jet lag)
• timing, intensity, and design must all be tailored to the circumstance • behaviour protocols for scheduled
dark periods
• employer needs to get workers' compliance
• special applications for clinical use
• consult specialists Arousal & Stress
(Section 2.3)
• avoid creating stressors: direct glare, excessive luminance contrast
• use high--frequency ballasts for fluorescent lights
• especially if sensitive populations present (e.g., children, migraine
Mediating Process Guidelines Comment
patients) Attention &
Appraisal (Section 2.4)
• create interest by integrating luminance variability with architecture
• also helps to extract information from environment
• highlight important elements • e.g. chalkboard • avoid emphasis on irrelevant cues • prevent distraction Affect, Expectations,
& Beliefs
• use meaningful luminance patterns to create interest
• extreme luminance patterns can become glary
(Section 2.5) • keep vertical surfaces bright • high reflectances help (e.g. light or white walls)
• use daylighting and windows where possible
• strongly preferred; also energy-efficient
• learn end--users' expectations & beliefs about lighting
• acceptance will be higher if the installation meets expectations • educate users before
implementing new technologies or designs
• vivid, personal information is best remembered, especially if the source is credible
Perceived Control (Section 2.6)
• consider individual controls to allow lighting tailored to needs
• especially in shared areas, or where needs change often • don't give more options than
occupants need/want
• remove additional stressors: educate users well, fix problems immediately
2.4 Attention and appraisal
The visual information we use to make judgements about the appearance of a space is based on patterns of light and dark and colour. It follows that lighting installations can contribute to those judgements. Environmental psychology research demonstrates that most people prefer views in which not everything is revealed, but in which the hidden parts fall into a coherent pattern [12]. Loe and Rowlands, knowingly or not, were consistent with this theoretical foundation in recommending that lighting design be consistent with architectural form, and that designers use luminance contrast to add visual interest [13].
2.5 Affect, expectations, and beliefs
The possibility that providing lighting that people prefer in order to create favourable emotional states (positive affect) is a focus of several current investigations, including one manuscript in preparation [14]. Whether or not this theory finds support, successful installations will incorporate or respond to the expectations and beliefs of occupants. Without this basis, lighting designers will face resistance to new designs and new technologies. For example, people who fear ill-health as a consequence of fluorescent lighting are less likely to adopt compact fluorescent lamps in their homes [15]. The basis in psychological theory for this effect has been reviewed elsewhere [16].
The state of the literature does not yet permit precise statements about luminous conditions that are preferred for various tasks, settings, and individuals, although efforts are being made to determine the limits [14]. Such general statements as may be made based on current knowledge are presented in Table 1; the literature is summarised in ref [5].
2.6 Perceived control
Perceived control in the psychological sense is about more than switches and dimmers. The issue concerns the understanding that one's actions can change the lighting conditions. It is related to the expectation that one's choices in this matter would improve the conditions. Evidence suggests that if the lighting conditions are good, control has few additional benefits; but if there are deficiencies in the lighting design then control can enable individuals to tailor the lighting to their needs [17] Others
warn, however, that in an already demanding environment, adding the need to control one's lighting can add an unwanted extra stressor [18]. Failing to educate occupants in how to use a new control system is one way to cause such a problem. Although the system might give many options to the individual, its very complexity can create concern that attempts to change the lighting will make matters worse -- conditions under which people generally prefer to have an expert make the choice for them [19].
3.0 Conclusions: Achieving Lighting Quality
The guidelines in Table 1 are obviously preliminary and incomplete. Our understanding is inadequate to attach specific values to the recommendations, such as the upper limit of luminance contrast that is desirable to provide interest without the maximum value becoming a glare source. Table 1 is provided merely as a starting point for moving from abstract research knowledge to specific design guidelines, to inspire researchers to formulate interesting new questions and designers to demand better guidance. One of the more serious limitations of these guidelines is that they do not include two of the dimensions of lighting quality, architectural and economic concerns. The basic approach to design guidelines, could, however, be the same in these areas. Processes to be considered in the economic sphere include installation, maintenance, and operation, as well as energy management. In the architectural sphere, one might use form, composition, and construction as the organising principles for guidelines.
It should be readily apparent to the reader that the advances made by lighting quality advocates have not had the effect of reducing lighting design to a 'paint by numbers' activity. If anything, it has served to clarify the complexity of the issues that the lighting designer must resolve. Better guidelines might summarise reams of general information about the achievement of various goals for the design, but they cannot specify the technologies used to deliver and control the light. Technologies change quickly, and there are often many ways to reach the recommended criteria. The designer's job is and will remain to determine, based on client needs, budget, energy use, and other contextual limits, the best way to achieve the desired lighting conditions for a particular architectural space. In creating research-based lighting guidelines, we can hope for a stronger linkage between the science and the art of lighting, but both will remain fundamental to providing lighting for people.
Acknowledgements
The author is grateful to Peter Boyce, Judi Heerwagen, Carol Jones, Stuart Kaye, David Loe, Terry McGowan, Naomi Miller and Guy Newsham for many conversations that contributed over time to the ideas presented here.
References
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