Lighting Quality and Energy-Efficiency Effects on Task Performance, Mood, Health, Satisfaction, and Comfort
Year: 1998
Type: article
Abstract: The adoption of energy efficiency measures in building codes places constraints on lighting designers that they fear will reduce the quality of the lit environment.This experiment was designed to test the hypothesis that lighting quality, as understood by lighting designers, affects the task performance, mood, comfort, health, and aesthetic judgements of office workers.Nine lighting systems were installed in a windowless, 83 m 2 (880 ft 2 ), open-plan office space containing six workstations.The designs combined three levels of lighting power density (LPD) and three levels of Designers' Lighting Quality (DLQ) (recessed troffers with prismatic lenses; recessed troffers with parabolic louvers; indirect or direct/indirect fixtures).In the low LPD options, the ambient lighting systems were supplemented with task lighting.Temporary office workers (292 in total) each worked for one day under one of the nine lighting conditions.In addition to morning and afternoon visual performance tests, they performed a variety of computer-based and paper-based tasks designed to be representative of modern office work, and completed questionnaires to assess satisfaction and impressions of lighting quality, mood, physical comfort, and social behaviours.The results show that energy-efficient lighting and good-quality lighting can be compatible.For computer-based work, under existing lighting power density limits, parabolic-louvered luminaires provide better verbal-intellectual and clerical task performance than recessed lensed luminaires.Verbal-intellectual task performance and visual performance were better under electronic ballasts than magnetic ballasts, regardless of lighting system.Résumé L'adoption de mesures de rendement énergétique dans les codes du bâtiment impose des contraintes aux éclairagistes qui, selon eux, risquent de réduire la qualité du milieu éclairé.On a conçu cette expérience dans le but de vérifier l'hypothèse selon laquelle la qualité de l'éclairage, comme l'entendent les éclairagistes, influe sur l'exécution des tâches, l'humeur, le confort, la santé et les jugements esthétiques des employés de bureau.Neuf systèmes d'éclairage ont été installés dans un bureau en espace fonctionnel sans fenêtre de 83 m 2 (880 pi 2 ) contenant six postes de travail.Les modèles combinaient trois niveaux de densité de puissance lumineuse (DPL) et trois niveaux de qualité «concepteur» de l'éclairage (QCÉ) (chemins lumineux encastrés avec verres diffuseurs prismatiques, chemins lumineux encastrés avec paralumes paraboliques, appareils indirects ou directs et indirects).Dans les cas de DPL faibles, les systèmes d'éclairage ambiant ont été complétés par un éclairage direct.Chacun des employés de bureau temporaires (292 en tout) a travaillé pendant une journée dans l'une des neuf conditions d'éclairage.En plus des essais de performances visuelles du matin et de l'après-midi, ils ont effectué une variété de travaux sur ordinateur et sur papier censés être représentatifs des travaux de bureau d'aujourd'hui et ils ont rempli des questionnaires pour évaluer la satisfaction et leurs impressions sur la qualité de l'éclairage, l'humeur, le confort physique et les comportements sociaux.Les résultats indiquent qu'un éclairage éconergétique peut être compatible avec un éclairage de bonne qualité.Dans le cas du travail sur ordinateur, dans les limites de densité de puissance lumineuse existantes, les luminaires à paralumes paraboliques donnent de meilleurs résultats pour les tâches verbales-intellectuelles et routinières que les luminaires à verres diffuseurs encastrés.On a obtenu de meilleurs résultats dans le cas des tâches verbales-intellectuelles ainsi que dans le cas du rendement visuel avec des ballasts électroniques plutôt que magnétiques, quel que soit le système d'éclairage. Lighting Quality and Energy-Efficiency Effects on Task Performance,Mood, Health, Satisfaction and Comfort Many jurisdictions have legislated energy codes that restrict building energy consumption for all uses, including lighting.1,4 Quality lighting systems today must meet or better these energy-use levels so that both the environment and resources are conserved (meeting long-term human needs), while still meeting immediate task, social, behavioural, aesthetic, emotional, health, and safety needs.Maintaining this balance is important to building owners, employers, and occupants, for lighting is an important feature in office design and furnishings.26,36 Although many lighting systems exist that meet energy-efficiency requirements, concern persists that more energy-efficient lighting design will result in poorer quality lighting.The absence of a common definition of lighting quality has been one impediment to progress on this issue.Veitch and Newsham 46,48 have proposed a behaviourallybased definition of lighting quality.According to this definition, lighting quality exists when the luminous conditions are suitable for the needs of the people who will use the space.They grouped these needs in six categories:• visual performance;• post-visual performance (e.g., reading, eating, sewing, walking);• social interaction and communication;• mood state (happiness, alertness, satisfaction, preference); • health and safety;• aesthetic judgments (assessments of the appearance of the space or the lighting).This approach is consistent with other environment-behaviour research, particularly that aimed at understanding relationships between working conditions and individual and organisational-level outcomes.For example, Rubin 30 conducted an extensive literature review and concluded that there existed no measures of organisational effectiveness and/or productivity relevant to micro-environmental design.He proposed that the best approach to developing such a measure would be to use a variety of subjective and objective measures.A review of the literature revealed only a weak understanding of the relationships between luminous conditions and these human needs.46,48 Poor research design, small sample sizes, and inappropriate use of statistical tests all mar the quality of the literature base.This experiment was designed to expand our understanding of lighting quality by relating lighting quality, as understood by lighting designers (Designers' Lighting Quality, DLQ), to behavioural measures from each of the six categories listed above.The experiment also examined the relationship between DLQ and lighting energy-efficiency, as represented by the lighting power density (LPD).Our working hypotheses were, first, that increasing DLQ would cause better outcomes on all dependent measures; and, second, that this relationship would be independent of LPD.That is, we predicted that low-LPD lighting systems, when selected and designed by professionals, could provide equivalent lighting quality to high-LPD systems.Any effect in which high-LPD systems produced better lighting than low-LPD systems would cast doubt on the wisdom of current energy-efficiency strategies for lighting.Method This experiment was a 3 x 3 (DLQ X LPD) factorial between-subjects experiment.There were three levels of DLQ (low, medium, and high, described below), and for each DLQ level there was a low LPD (8.0-9.3W/m 2 [0.7-0.9W/ft 2 ]), medium LPD (11.3-13.3W/m 2 [1.1-1.2W/ft 2 ]) and high LPD (19.8-25.1 W/m 2 [1.8-2.3W/ft 2 ]) variant.Participants Participants (142 women and 150 men, aged 18 to 61 years.)were recruited through a temporaryemployment agency, which pre-screened potential participants to ensure that they met the following criteria: minimum 18 years of age; normal or corrected-to-normal vision; normal hearing; no mobility impairments; experience with Windows™-based word-processing and spreadsheets; and, fluency in English.The participants were paid for their participation at the standard rate for the type of clerical work characterised by the tasks.Participants were recruited, informed, and debriefed according to the exacting standards of the institution's Human Subjects Research Ethics Committee.Each participant was randomly assigned to one of the nine lighting conditions and worked under that lighting system for one day on a variety of computer-and paper-based office tasks and questionnaires.Random assignment to experimental conditions distributes individual differences equally across the groups; therefore, if between-group differences in outcome measures are found, they may be attributed to the experimental manipulation.7,20 Setting The experiment took place in a mocked-up 12.2 x 7.3 m (40 x 24 ft) office designed for acoustics, lighting,
Authors: J.A. Veitch, G.R. Newsham
Institution: National Research Council Canada
Language: English
Subfield: Social Psychology
Field: Psychology
Domain: Social Sciences
Open Access status: bronze
Funder: Natural Resources Canada
OpenAlex ID: W1995884091