Jan Wienold

Gaze and discomfort glare, Part 1: Development of a gaze-driven photometry

Discomfort glare is a major challenge for the design of workplaces. The existing metrics for discomfort glare prediction share the limitation that they do not take gaze direction into account. To overcome this limitation, we developed a ‘gaze-driven’ method for discomfort glare assessment. We conducted a series of experiments under simulated office conditions and recorded the participants’ gaze using mobile eye tracking and the luminance distributions using high dynamic range imaging methods. The two methods were then integrated to derive ‘gaze-centred’ luminance measurements in the field of view. The existing ‘fixed-gaze’ and the newly developed ‘gaze-driven’ measurement methods are compared. Our results show that there is a significant difference between the two methods. In this paper, the procedure for integrating the recorded luminance images with the recorded gaze dynamics for obtaining gaze-centred luminance data is described. This gaze-centred luminance data will be compared to the subjective assessment of glare in Part 2 of this study.

Adequacy of Immersive Virtual Reality for the Perception of Daylit Spaces: Comparison of Real and Virtual Environments

ABSTRACT This article presents a novel experimental method that uses a virtual reality (VR) headset, aiming to provide an alternative environment for the conduction of subjective assessments of daylit spaces. This method can overcome the difficulty of controlling the variation of luminous conditions, one of the main challenges in experimental studies using daylight, and its novelty lies in the implementation of physically based renderings into an immersive virtual environment. The present work investigates the adequacy of the proposed method to evaluate five aspects of subjective perception of daylit spaces: the perceived pleasantness, interest, excitement, complexity, and satisfaction with the amount of view in the space. To this end, experiments with 29 participants were conducted to compare users’ perceptions of a real daylit environment and its equivalent representation in VR and test the effect of the display method on the participants’ perceptual evaluations, reported physical symptoms, and perceived presence in the virtual space. The results indicate a high level of perceptual accuracy, showing no significant differences between the real and virtual environments on the studied evaluations. In addition, there was a high level of perceived presence in the virtual environment and no significant effects on the participants’ physical symptoms after the use of the VR headset. Following these findings, the presented experimental method in VR seems very promising for use as a surrogate to real environments in investigating the aforementioned five dimensions of perception in daylit spaces.

Review of Factors Influencing Discomfort Glare Perception from Daylight

ABSTRACT Because well-being is becoming a major challenge in construction alongside energy efficiency, there is an increasing need to be able to quantify discomfort in buildings. In the case of discomfort glare, the kind of glare provoking an irritating or distracting effect, no current indices can properly explain the high variability existing between individuals’ discomfort glare perceptions. This is due to the fact that some of the factors influencing discomfort glare perception are still unknown and the mechanism behind the discomfort glare process is not well understood. Therefore, this article aims to review the factors potentially influencing discomfort glare perception from daylight. Every factor having been studied at least once for its potential influence on discomfort glare perception has been listed, described, and analyzed. Furthermore, this study categorizes the influence of these factors on discomfort glare by introducing an influence indicator based on the number of studies having investigated the factor, the sample size of these studies, and the agreement between them. The suggested categories rate a factor influence as “almost certain,” “more likely,” “somewhat likely,” “inconclusive,” “somewhat unlikely,” “less likely,” or “almost certainly null.” Tables summarize the main information about the studies and the influencing factors. As expected, factors almost certainly influencing discomfort glare perception are the luminance of the glare source, adaptation level, contrast effect, and size and position of the glare source. In contrast, factors that almost certainly do not influence discomfort glare perception are the gender and optical correction of the observer. All other factors from the list of 30, such as the attractiveness of the view through the window or the culture of the observer, require additional studies to determine whether or not they influence discomfort glare perception.

Correspondence: Investigation of Evalglare software, daylight glare probability and high dynamic range imaging for daylight glare analysis:

I have read with great interest the paper ‘Investigation of Evalglare software, daylight glare probability and high dynamic range imaging for daylight glare analysis’ and the corrigendum to it. As author of the Evalglare software, I’m glad to hear that the software tool is helping researchers and planners in evaluating discomfort glare. In Section 3.3 of the paper, the authors discuss the illuminance calculation in Evalglare and conclude that the accuracy of Evalglare is questionable based on deviations between measured illuminance values and image-calculated illuminance values. This conclusion seems incorrect as a fully documented validation study shows that Evalglare calculates the illuminance correctly for all supported projection methods. In this validation study, Evalglare-calculated values were compared with analytically determined values as well as with values calculated from images by an alternative method that was provided by the author of RADIANCE. Only marginal differences between these methods and analytically derived values were found. Therefore, a deviation described by the authors between measured illuminance values and calculated values is caused by other reasons than an inaccuracy in the implemented algorithms of Evalglare. In fact, based on the results provided in the paper and in the corrigendum, it seems that even after the corrections described in the corrigendum are applied, significant deviations between measured and calculated illuminances still occur. Comparing the calculated illuminance values of Table 6 of the corrigendum and the measured illuminance values given in Table 2 of the paper, a relative deviation of þ40% for Scene 1 (76.3 lux vs. 54.6 lux), of þ36% of Scene 2 (4096 lux vs. 3014 lux) and 82% (10,390 lux vs. 58,125 lux) for Scene 4 can be observed. Such deviations are significant enough to raise new questions, given that they actually cannot be explained by inaccuracies in Evalglare (cf. validation study), such as: What is the probable source of these deviations? Does the limited range of EV-stops ( 2) applied during the high dynamic range (HDR) generation process impact the deviations? Do these deviations question the main findings of the paper, namely, the inconsistency between different glare metrics (which may be impacted differently by the yet-to-beidentified source of error)? Answers to these questions would improve the understanding of the outcomes and clarify the scope of application of the paper.