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Office lighting appraisal, performance, and well-being: a linked
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Published in: Proceedings of the CIE 26th Session, Beijing, 4 July – 11 July 2007 (CIE178:2007, Vol. 1, pp. D3-61 – D3-64). Vienna, Austria: Commission Internationale de l.Eclairage.
OFFICE LIGHTING APPRAISAL, PERFORMANCE, AND
WELL-BEING: A LINKED MECHANISMS MAP
Veitch, J. A.*; Newsham, G. R.*; Boyce, P. R.†; Jones, C. C.‡
* National Research Council of Canada / † Rensselaer Polytechnic Institute, USA / ‡ Battelle – Pacific Northwest National Laboratory, USA
ABSTRACT
Most would agree that a high-quality lighting installation provides good task visibility and contributes to the attractiveness of the space. In two experiments in a simulated office space, temporary office personnel worked under one of six lighting conditions for a day. Combined results from two statistical approaches show that people who perceived their office lighting as being of higher quality rated the space as more attractive, reported more pleasant mood, and showed greater well-being at the end of the day. Direct-indirect lighting and personal control were favoured. Lighting conditions that improved visibility also improved task performance.
Keywords: direct-indirect luminaires, lighting quality, personal control, satisfaction
1. INTRODUCTION
Lighting practice based on the principles of maximizing visual performance and avoiding visual discomfort [1,2] has ensured that it is rare today to find offices lit in such a way that either visual performance is limited or visual discomfort occurs. However, offices that are perceived to be gloomy and uninteresting remain common, a fact that has been the impetus behind the burgeoning field of lighting quality [3,4,5]. One thing agreed-upon concerning lighting quality is that a high quality lighting installation needs to consider not just the visibility of the tasks but the appearance of the space. This report describes a study into the effect of varying levels of lighting quality on the task performance of office workers and their health and well-being.
The study consisted of two experiments in which groups of temporary office workers came into a simulated open-plan office to work for a day at a time under a lighting condition chosen to exemplify either standard practice or better practice as judged by lighting professionals. The first experiment contrasted four lighting conditions; the second compared two lighting conditions. Some of the lighting conditions in the first experiment provided individual control over the workstation lighting; others did not. In both experiments the participants completed a battery of tasks whose components are typical of office work (typing, proofreading, evaluating written work) and several questionnaires concerning visual and physical comfort, mood, satisfaction with the work environment and the lighting, and judgements of the appearance of the space.
The questionnaires and tasks were chosen in order to provide measurements of each concept in a linked mechanisms map [7]. This map, shown in Figure 1, set out an expected set of relationships between the variables; it is a proposal for explaining how the expected effect of lighting conditions would influence health, well-being, and performance.
Figure 1. Proposed linked mechanisms map.
Veitch et al., Appraisal Mechanisms
This paper reports on tests of the connections in the linked mechanisms map using data for perceptions, feelings, and performance during the latter part of the workday. Detailed results for the effects of lighting conditions on all dependent variables, taking into account changes over the workday, have been reported elsewhere [8], as have analyses of the use of individual controls [9].
2. METHOD
2.1 Setting and lighting conditions
Complete details of the experimental conditions are provided in references 6 and 8. The experiments took place in a leased office space in Albany, New York. The space was furnished as a typical small open-plan office with nine cubicles. Over the two experiments there were six different lighting configurations, all of which were compliant with existing North American standards for office lighting. In Experiment 1 there were recessed parabolic-louvered luminaires; suspended linear direct-indirect luminaires (at ~600 lx desktop illuminance); suspended linear direct-indirect luminaires with a switchable desk lamp; and, suspended workstation-specific direct-indirect luminaires with individual workstation dimming for the direct portion. Experiment 2 contrasted recessed prismatic-lensed luminaires and suspended linear direct-indirect luminaires dimmed to 400 lx desktop illuminance.
2.2 Procedure
Participants were hired from an office temporary services agency. In Experiment 1, they were randomly assigned to one of four lighting conditions. A subset of participants in Experiment 1 returned to participate in a second condition on a later day. In Experiment 2, a separate set of participants were randomly assigned to one of two lighting conditions.
In both experiments, participants worked under the given lighting condition for a full 7,5-hr day, completing a set of tasks and questionnaires. The tasks were selected to be representative of components of office work. Complete details are available in reference [8].
3. RESULTS
3.1 Lighting condition effects
In reference [8] we reported the extensive analyses of variance and nonparametric tests we conducted to test the effects of the various lighting conditions on all of the dependent measures. Several findings are relevant here because they demonstrate links in the map: The lighting from indirect luminaires were rated as being comfortable by more people than that from direct-only luminaires (~80% vs. ~70%). Individually controllable workstation-specific lighting was rated as being comfortable by over 90% of participants. Lighting conditions that improved the visibility of the tasks led to better task performance. Individual control over lighting beneficially affected motivation and well-being (dotted lines in Figure 2).
3.2 Linked mechanisms: Mediated regression analysis
Broadly speaking there are two parallel paths through the map, one leading through appraisal (the ‘Appraisal Path’) and the other through vision (the ‘Vision Path’) although there are some cross links. We used the statistical techniques for mediated regression analysis set out by Baron and Kenny [10] to test the causal chains described in the map. This is a logical sequence of multiple regression analyses. To take one example, the chain from appraisal → preference → mood: One first regresses preference on appraisal. One next regresses mood on appraisal. Finally, one regresses mood on preference and appraisal together. All three steps must return statistically significant results. At the third step, with two predictors, one looks for the first step variable (appraisal) to have a smaller effect size than it had at the second step, when it was entered alone; the mediating variable (preference) must also have a statistically significant effect on the outcome (mood).
We began the mediation chain starting from the level of appraisal, visual comfort, and visual capabilities. Note that these analyses did not include the lighting conditions as variables. The data were those from the last session of the workday, after the participants had had six hours’ exposure to the lighting conditions, to avoid novelty effects. For the final outcomes, we separately examined three indicators of health and well-being: overall discomfort ratings, environmental
Veitch et al., Appraisal Mechanisms
satisfaction ratings, and performance satisfaction ratings. For task performance, we examined length of rest breaks, speed of responding to a prompt (attention), typing, overall cognitive performance speed, and correct article categorizations. For each intervening concept in the linked mechanisms map, we chose one variable as an exemplar. The antecedent variables were lighting quality ratings (appraisal); attractiveness ratings (preference); pleasure ratings (mood); speed of random responding on a target-detection task (motivation); visual discomfort ratings (visual comfort); composite visual performance (visual capabilities); and, environmental competence ratings (competence). We repeated the analyses for three independent data sets: Experiment 1 first visit (N=151); Experiment 1, second visit (N=36), and Experiment 2 (N=80). This provides internal replication, and strengthens our confidence in the results.
Overall, the results were strongest for the Appraisal Path, leading through preference and mood to health and well-being. This path showed clear evidence of mediated effects in all three data sets, explaining large amounts of variance in most cases. The evidence for visual capabilities on task performance was less dramatic, likely because the tasks were not visually challenging; however, as expected, people with lower visual capabilities did poorer on the typing task.
Links between the two paths did not work as expected. Visual comfort and visual capabilities were unrelated here, likely because most people experienced high visual comfort. There was an unexpected negative relationship between preference and motivation that we cannot explain; however, motivation did positively predict several types of task performance. These relationships were mostly small to medium in size.
4. DISCUSSION
We combined all of the results from the various analyses and the two experiments into one modified linked mechanisms map, shown in Figure 2.
Figure 2. Final linked mechanisms map, showing lighting condition effects with dotted lines, and mediated regression tests with solid lines. The lighter-weight lines show a small effect that was not previously predicted.
Overall, people who rated the lighting as of higher quality (regardless of the type of lighting they experienced) considered the space to be more attractive, were happier, and had better health and well-being in the form of less discomfort and greater satisfaction with their environment and their work. This is the first time the complete path from lighting conditions to feelings of health and well-being has been demonstrated. This is a first step towards the demonstration that better-quality lighting can support organizational productivity. Other researchers have demonstrated that greater environmental satisfaction leads to greater job satisfaction [11] and that higher job satisfaction leads to greater organizational commitment and reduced intent to turnover [12].
Veitch et al., Appraisal Mechanisms
Organizations whose employees are more satisfied show better customer satisfaction and business unit performance [13].
Lighting conditions that support employees, then, should achieve both high task visibility and favourable appraisals of lighting quality. These experiments found that direct-indirect lighting systems, particularly those offering control over the direct component, are most likely to meet both of these goals [8].
REFERENCES
[1] Rea, M. S., & Ouellette, M. J. (1991). Relative visual performance: A basis for application.
Lighting Research and Technology, 23(3), 135-144.
[2] Boyce, P. R. (2003). Human factors in lighting (2nd ed.). London: Taylor & Francis.
[3] Veitch, J. A. (1998). Commentary: On unanswered questions. In J. A. Veitch (Ed.),
Proceedings of the First CIE Symposium on Lighting Quality (Vol. CIE-x015:1998, pp.
88-91). Vienna, Austria: CIE.
[4] Veitch, J. A., & Newsham, G. R. (1998). Determinants of lighting quality I: State of the science. Journal of the Illuminating Engineering Society, 27(1), 92-106.
[5] Veitch, J. A., & Newsham, G. R. (1998). Lighting quality and energy-efficiency effects on task performance, mood, health, satisfaction and comfort. Journal of the Illuminating
Engineering Society, 27(1), 107-129.
[6] Boyce, P. R., Veitch, J. A., Newsham, G. R., Myer, M., & Hunter, C. (2003). Lighting quality
and office work: A field simulation study (PNNL 14506). Richland, WA, USA: Pacific
Northwest National Laboratory.
[7] Wyon, D. P. (1996). Indoor environmental effects on productivity. In K. Y. Teichman (Ed),
Proceedings of IAQ '96: Paths to Better Building Environments (pp. 5-15). Atlanta, GA:
American Society of Heating, Refrigerating, and Air Conditioning Engineers.
[8] Boyce, P. R. et al. (2006). Lighting quality and office work: Two field simulation experiments. Lighting Research and Technology, 38(3), 191-223.
[9] Boyce, P. R. et al. (2006). Occupant use of switching and dimming controls in offices.
Lighting Research and Technology, 38(4), 358-378.
[10] Baron, R. M., & Kenny, D. A. (1986). The moderator-mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of
Personality and Social Psychology, 51(6), 1173-1182.
[11] Charles, K. E., Veitch, J. A., Farley, K. M. J., & Newsham, G. R. (2003). Environmental
satisfaction in open-plan environments: 3. Further scale validation (IRC-RR-152). Ottawa,
ON: National Research Council of Canada, Institute for Research in Construction.
[12] Carlopio, J. R. (1996). Construct validity of a physical work environment satisfaction questionnaire. Journal of Occupational Health Psychology, 1, 330-344.
[13] Harter, J. K., Schmidt, F. L., & Hayes, T. L. (2002). Business-unit-level relationship between employee satisfaction, employee engagement, and business outcomes: A meta-analysis.
Journal of Applied Psychology, 87(2), 268-279. ACKNOWLEDGEMENTS
This investigation was supported by the Light Right Consortium, managed by Pacific Northwest National Laboratory under RFP # 404141, through contracts to Rensselaer Polytechnic Institute’s Lighting Research Center (RPI # A11106) and the National Research Council of Canada Institute for Research in Construction (NRC # 44-B3214). This phase of the Light Right Consortium was supported by the Alliance to Save Energy, the Illuminating Engineering Society of North America, the International Association of Lighting Designers, the International Facility Management Association, Johnson Controls, the National Electrical Manufacturers Association, the New York State Energy Research and Development Authority, Steelcase, Inc., the US Department of Energy, and the US Environmental Protection Agency.
Authors:
Jennifer A. Veitch, Ph.D.
NRC Institute for Research in Construction National Research Council Canada Building M-24, 1200 Montreal Road Ottawa, ON K1A 0R6 Canada tel. +1-613-993-9671
Veitch et al., Appraisal Mechanisms
e-mail: jennifer.veitch@nrc-cnrc.gc.ca
© 2007, Battelle Memorial Institute / Rensselaer Polytechnic Institute / National Research Council Canada
