Visual Discomfort Assessment in Office Environments: Light-induced Physiological Responses and Visual Performance

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Skates, Henry

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Isoardi, Gillian

Fernando, Ruwan A

Hine, Trevor J

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2020-02-18
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Abstract

The benefits of exploiting natural light in office environments are numerous, ranging from enhancing human mood, satisfaction, productivity, health and wellbeing to reducing the energy consumption required for electric lighting. However, excessive sunlight remains problematic in terms of glare and undesirable visual discomfort. The existing discomfort glare predictive models are mainly derived from conventional subjective evaluations and photometric measurements and there is always a degree of uncertainty and bias associated with subjective measurements. For this reason, a more promising research method of pairing subjective assessments with objective measures was proposed as an alternative approach. In this research, a comprehensive method is utilised to investigate a full range of potential objective measures of visual discomfort, including involuntary light-induced physiological responses, eye movements and visual performance. This method couples physiological measurements and visual performance assessments with conventional photometric measurements and subjective evaluations. For this investigation, an experimental study was carried out for three different scenarios: low, medium, and high glare probability. Participants were required to perform simulated office tasks, while an eye-tracker recorded the pupil and ocular data. The ocular and pupillary metrics extracted from these data were: mean Pupil Diameter (PD), Pupillary Unrest Index (PUI), spontaneous Blink Rate (BR), Blink Amplitude (BA), number of fixational eye movements during reading (Fixation Rate (FR)), average Fixation Duration (FD), and Eye Convergence (EC). In addition, for each participant, the Combined Visual Performance (CVP) and Combined Reading Performance (CRP) were measured during the experiment. Analyses of variance were undertaken to determine differences on all measures among three lighting conditions with low, medium and high levels of visual discomfort. The results show significant differences between the high and low discomfort groups across most of the dependent variables. In particular, participants in high discomfort conditions exhibited a higher FR, lower BR, higher BA, smaller mean PD and poorer CVP than participants in both the low and medium discomfort conditions. This indicates that the studied physiological measures can be used as an indicator of high levels of glare or visual discomfort. Nevertheless, EC and CRP were not affected by lighting conditions. The CRP was better when the FD and the PUI were lower. Correlation and multiple regression analyses suggest that PUI, BA, FR and mean PD could be used as an indicator of visual discomfort, however, PUI and BA was shown to be predicted better with contrast measures and FR and PD with luminance and illuminance levels in the visual field. In addition, investigation of subjective evaluations has shown that visual comfort ratings may be a more reliable metric in reflecting visual discomfort experienced by the occupants. This holistic approach offers new insight into the application of objective measures in assessment and prediction of visual discomfort, by advancing knowledge on various physiological and ocular responses and identifying the most sensitive indicators and relating all of this to visual and reading performance at work stations.

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Thesis (PhD Doctorate)

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Doctor of Philosophy (PhD)

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School of Eng & Built Env

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The author owns the copyright in this thesis, unless stated otherwise.

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Subject

natural light

office environments

visual discomfort

discomfort glare predictive models

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