Discomfort glare from daylighting: study of factors influencing discomfort glare perception and validation of a universal discomfort glare index

Pierson, Clotilde [UCL] Bodart, Magali [UCL] Cauwerts, Coralie [UCL] Wienold, Jan [EPFL]

Nowadays, no current index can properly explain the high variability existing between individuals’ discomfort glare perception. The mechanism behind the discomfort glare phenomenon is not well understood as some of the factors influencing this phenomenon are still unknown. A large literature review has shown that in addition to the physical quantities currently used in discomfort glare indices, other variables such as contextual, physiological, or even psychological factors, could influence the degree of perceived discomfort glare. The aim of this research project is therefore to determine which factors, whether physiological, psychological, contextual or physical, have a real and significant influence on discomfort glare perception in daylighting. Subsequently, these factors can be compiled in a new discomfort glare model or included in the Daylight Glare Probability, which is the most accurate index at present. During the first stage of the project, potential factors were identified thanks to a large literature study. Every factor having at least been the object of an experiment as a potential element influencing discomfort glare perception has been reviewed. Its influence was classified as either certain, probable, improbable, uncertain or nonexistent. The second stage consists in collecting a large dataset of objective and subjective discomfort glare evaluations through a field experiment in offices using daylighting. The office occupants answer a questionnaire to assess various factors, such as their age, self-assessed glare sensitivity or color of the eyes and to evaluate discomfort glare from daylight in their office. In the meantime, luminance and illuminance measurements as well as HDR images (fig. 1) are collected. Since this research project focuses on the influence of culture on discomfort glare perception, this experiment will be conducted in Chile, Belgium and Japan. These countries have been chosen considering the climate and cultural diversity requirements and because of the local presence of competent teams in the field of daylighting. In total, a dataset of around two hundred investigated offices should be achieved. The last stage of the project involves comparisons between the gathered objective and subjective discomfort glare evaluations through statistical analyses. These analyses are aimed at highlighting factors having an influence on discomfort glare perception. The expected result of this research project is a more accurate and universal discomfort glare evaluation model for daylighting, including validated physiological, psychological or contextual factors. A better understanding of the discomfort glare mechanism should also be achieved.