Search

This paper investigates the impact of transmittance level and layout variations of semi-transparent photovoltaics (STPV) on both energy performance and occupancy-based visual and thermal comfort, simulating a reference office with a fully south-oriented glazed surface. Four transmittance levels (20, 30, 40 and 50%) were investigated, first uniformly distributed on the full glazing (i.e., one specific transmittance for the entire glazing) and then considered in combination (i.e., with the glazing divided in equal-height bands with different transmittance levels). Simulations were conducted in three climatic conditions: temperate (Geneva), hot-arid (Casablanca) and cold (Helsinki). Following the proposed energy and occupancy-based visual and thermal comfort analysis, the best design option for both Geneva and Helsinki climate resulted the 2-level STPV design variation with 50% visible transmittance on top of the glazing. In Casablanca, the 1-level design variation with the lowest visible transmittance (20%) uniformly distributed resulted as the best choice. This work, besides offering a first exploration of the relationships between climatic context and STPV design variations, describes a spatial multi-criteria analysis method that could be applied for the evaluation of other glazing technologies.

In our daily lives we are exposed simultaneously to multiple sensory stimuli, such as visual, thermal, acoustic and olfactory. Experienced together, they shape our perception of the environment and determine our comfort. In indoor environments, stimuli are affected by construction features such as material, openings, form, size and colour. However, standards and guidelines for the design of buildings, together with the majority of scientific investigations on indoor factors, focus on independent stimuli, considering visual, thermal, acoustic and air quality issues separately. The problem lies in the fact that multiple sensory stimuli, other than affecting our general perception and comfort when experienced in combination, can result in cross-modal effects, whenever a stimulus influences a non-related perception. It could happen, for example, that a sound affects people’s thermal perception or that the thermal environment influences the perception of the indoor air quality. To further the understanding of cross-modal effects, it is therefore necessary to study multiple indoor stimuli in combination. With a particular focus on visual and thermal stimuli, this contribution investigates the interactions between daylight and temperature. First, daylight transmitted through coloured glazing (henceforth referred to as “coloured daylight”) and then different illumination levels of daylight are investigated, in combination with indoor temperature levels. To explore both cross-modal perceptions, the study focuses on the effect of daylight (both “coloured daylight” and daylight levels) on thermal perception and on the effect of temperature levels on visual perception of daylight. For the investigation, two experiments were conducted in a semi-controlled test room, able to set specific temperature levels and with the possibility to apply filters on the South and the North openings. In the first experiment, filters were coloured (blue, orange, against a reference neutral one with similar transmittance levels), while in the second one, filters were neutral with different transmittance levels. Results from both experiments showed that cross-modal effects do occur between daylight and temperature, with temperature influencing visual perception, and colour and quantity of daylight affecting thermal perception (e.g., people exposed to blue daylight were significantly colder and less comfortable compared to those exposed to orange and neutral, with p < 0.05 after linear mixed-model analysis). These findings highlight that indoor factors should not be considered in isolation and that researchers and designers should see the indoor environment as a whole, with all the sensory stimuli simultaneously contributing to shape our multi-sensory experience.

In a context where lighting standards are developed based on glare indices, no study has ever investigated that these indices could be used analogously for subjects having different cultures and living in different climates. The wide variability existing between individuals’ discomfort glare perceptions suggests, however, that some of the factors influencing discomfort glare perception are still unknown, and culture might be one of them. This paper aims to determine the existence of differences between the discomfort glare perceptions of Belgians and Chileans. A field study was conducted in Chile and Belgium, for which a total of 288 measures of the lighting environments and subjective glare assessments were collected. Statistical analyses of the Belgian and Chilean datasets showed that Chileans perceive discomfort glare differently than Belgians. It is therefore hypothesised that existing discomfort glare indices might not be suited for Chilean subjects accustomed to a different type of lighting environment.

Relatively recent cultural and technological changes, particularly in Westernized societies, have led to habitat and lifestyle shifts that have gradually estranged us from daylight. Although human beings are resilient and appear able to cope with extreme variations in environmental and living conditions, this process of separation can have negative impacts on health and well-being. Further research is essential in order to understand the impact of these changes and to initiate corrective measures, from changes in lifestyle and cultural attitudes to adjustments in the built environment and technology. This section explores these issues and the range of possible solutions.

This contribution focuses on perforated façades, investigating the effect of the façade and the resulting daylight pattern on the perceived spatial ambiance. The daylight conditions, as well as the geometry and regularity of the façade pattern are manipulated in an immersive virtual space, producing different conditions. A preliminary study was conducted, where subjective evaluations of the virtual space were recorded across six variations of façade pattern and sky type. The results indicate that the façade pattern characteristics have an impact on the perceived spatial ambiance, underlining the need to investigate further the perceptual aspect of the spatial and temporal diversity of light in space through experimental studies.

Exposure to daylight has much to offer and should be optimised to maximise its potential. In order to harvest its benefits, any visual discomfort from daylight should be anticipated and minimised. Hence, there is the need to predict discomfort from daylight glare. While more than 20 models for predicting discomfort from daylight glare have been developed, none accurately predict it. The inclusion of additional factors in the models may improve the predictions. One such factor is the socio-environmental context of the observer. This study compares the evaluations of discomfort glare from daylight for office buildings in four socio-environmental contexts: Chile, Belgium, Japan and Switzerland. The evaluations of discomfort glare, each consisting of subjective assessments and physical measurements of a view condition, were collected at the office desks of 401 participants, although only 211 responses were used in the analyses due to exclusion rules. The results do not suggest evidence of an influence of socio-environmental context on discomfort from daylight glare. In other words, the participants in this study perceived discomfort glare similarly, regardless of their socio-environmental context.

Within the framework of a study investigating interactions among indoor environmental factors, two experiments were conducted on the effects of visual stimuli on thermal perception. Thermal responses were recorded with two methods, one quantitative via physiological measurements and a subjective one using a questionnaire. The questionnaire was developed on the basis of the standard EN ISO 10551 (2001-06-01) and recent publications on thermal comfort [1]–[3]. Two types of measurement scales were used, i.e., Likert-type and visual analogue. The first type was used for the questions about the thermal sensation, thermal comfort and thermal preference of the subjects and for the thermal sensation of their body parts (hands, feet and body). The only visual analogue scale in the questionnaire referred to the acceptability of the local climate in the room where the experiment was conducted. Different outcomes were recorded for the survey questions as they assess different aspects of thermal perception, confirming the outcome of previous studies [4], [5]. The comparison between Likert- and visual-analogue scales shows a much broader variety of responses for the visual analog scale. We assume that this is due to the nature of the measurement technique that allowed fine-tuned judgement of the indoor climate on a scale from 0 (acceptable) to 100 (unacceptable). The Likert-type scales of the other questions, on the other hand, gave the chance to choose only among five or seven fixed answers, leading to responses much more restricted around particular values. As an outcome for the specific topic of our research (i.e., the study of interactions between visual and thermal factors), investigating in general small effect size, we argue that a measurement scale leading to a bigger variety of responses is more suitable. The development of a single value incorporating several responses from different questions is currently under discussion.

A gaze-driven methodology for discomfort glare was developed and applied for glare evaluation. A series of user assessments were performed in an office-like test laboratory under various lighting conditions. The participants’ gaze responses were recorded by means of mobile eye tracking while monitoring photometric quantities relevant to visual comfort using HDR luminance imaging. The integration of the luminance images coupled with eye-tracking methods enabled us to use gaze-centred luminance distribution to have an accurate estimate of the light received at the eye. Using a novel gaze-driven approach, a unique database was created as a basis to investigate the gaze direction dependencies of visual comfort. Here we compare the proposed gaze-driven approach with two other approaches based on fixed-gaze assumptions: gaze fixating on the task area, and gaze shifted 45 ° towards the window area. The results show that there is a significant difference between luminance distributions driven by gaze and those based on fixed-gaze assumptions, indicating a potentially important impact on glare assessment results as well.

This report presents the methodological approach and key findings of the eCOMBINE project (“Interaction between energy use, COMfort, Behaviour, and INdoor Environment in Office Buildings”). In this project, we develop an integrated approach to study the cause-effect relationships between occupant perception and behaviour, combined multi-domain indoor environmental factors (thermal, IAQ, visual and acoustic), and energy use. The eCOMBINE project relies on a mixed experimental approach that combines environmental measurements in the open-space office space with subjective responses from the building occupants. The eCOMBINE framework was applied to two Swiss pilot case studies located in Lausanne (Building A) and Geneva (Building B) with 13 and 31 participants, respectively. Based on data collected in these two open space offices, the outcomes of this work reveal relationships between global environmental stimuli (PART A), multi-domain environmental perceptions in real office settings (PART B), perceived multi-domain motivations behind human-building interactions (PART C), and energy use (PART D). Building simulations with measurement-based input further highlight energy performance gaps between the actual operation (based on real/tracked behaviour of occupants) with respect to recommended simulation input by Swiss standards.

Designing the buildings that facilitate optimum utilization of daylight is desirable for its many benefits [1], [2] yet challenging due to other intrinsic properties of daylight responsible for over-heating and discomfort glare [3]. Discomfort glare has been studied for several decades, although current empirical glare models are unable to account for the inter-individual differences in glare perception[4]. The complex and multidisciplinary nature of the phenomenon involves the fields of ophthalmology, lighting engineering, neuroscience but these fields remain quite disconnected from one another, which further adds to the slow progress in understanding this phenomenon [5], [6]. It is, therefore, necessary to incorporate interdisciplinary approach to anticipate what creates or influences the perception of discomfort glare from daylight. We aim to contribute to furthering this understanding by evaluating the discomfort glare perceived by the users in relation to eye morphology, with a dedicated focus on the macular pigment (MP) in the retina (Figure 1), an ocular characteristics shown to influence visual performance [4]. Figure

In industrialized countries, people spend on average 85-90% of their time indoors (1). For this reason, major efforts are being made to understand and control the factors which affect people’s comfort, health and well-being inside buildings (2). The indoor environmental quality is characterized by four main parameters, i.e., indoor air quality, acoustic ambience, visual and thermal conditions. The human senses allow people to perceive the environment and estimate their comfort and acceptability with respect to these four indoor environmental factors. For this reason, the evaluation of indoor comfort requires a thorough understanding of how humans (intended as beings characterised by a body and mind) perceive and respond to these environmental parameters (3). Over the last century, studies have considered only one single factor at a time of the indoor environment with the aim to identify relationships between the single component and human comfort. These studies resulted in comfort models (e.g., thermal comfort) (4), standards, guidelines (5–8) and quantitative indices (9) which provided threshold values for light, temperature, noise and air quality. Current building design and technologies devoted to control the indoor environment are designed on supposedly independent effects of visual, thermal and other factors (10). Yet, human sensory systems are not modular, but integrate and respond to environmental factors simultaneously. Moreover, such environmental factors commonly occur in combination. It becomes clear that no single parameter of the indoor environment can be evaluated on its own. Thus, to improve our understanding of the influence of environmental parameters on human responses and perceptions in indoor environments, it is necessary to study their combined effects. Predicting the integral building performance in terms of comfort is a complex task. For this reason, to progress with global comfort knowledge it is necessary to start with the study of the interactions of two factors at a time (11). This Ph.D. research focuses on the interaction between visual and thermal stimuli on comfort perception and performance by means of experiments in an office-like test room in EPFL campus and validation in field studies. In particular, it analyzes the effect of visual variables on the perceived thermal comfort and of thermal variables on the perceived visual comfort, beside their interactive influence on performance. Three different experiments are planned, analyzing the mutual influence of the following parameters on thermal and visual comfort perception: (i) coloured daylight and temperature, (ii) illuminance level and temperature (iii) glare and temperature. The first experiment about the influence of coloured daylight on thermal comfort perception and of temperature on colour acceptability and preference has started in November 2016.

Although fabrics are widely used as shading devices, reliable simulation models are rather rare and therefore the choice of a fabric with appropriate material characteristics is difficult. This paper presents a simulation model, which can be applied to most of the common available fabric shading materials. Furthermore a comprehensive simulation study has been conducted in order to derive simple to use tables for the selection of appropriate shading properties for a designer. These tables enable the user to select the "right" fabric according to a combination of multiple boundary conditions (location, orientation, window sizes, user positions).

The evaluation of indoor comfort requires a thorough understanding of how human occupants perceive four indoor environmental factors: visual conditions, air quality, acoustic ambience and thermal conditions. Recent studies have found that overall comfort is more than the average effects of these four parameters. Beside their main effects, their mutual interactions play an equally important role in the perception of comfort. Thus, to progress regarding our understanding of global comfort, more effort is needed to further investigate the interactions between indoor environmental factors. For this kind of perceptual evaluation, it is necessary to conduct user studies. In these, subjects’ evaluations need to be recorded in addition to the physical parameters that provoke them. Therefore, the sensitivity of people to their environment is the principal parameter around which the studies should be designed. This paper presents a first evaluation of the sensitivity of people to visual and thermal parameters in real office environments to establish a groundwork for future investigations. From this cross-sectional observational study, we concluded that possible effects of interactions between factors are difficult to see when the conditions are more or less comfortable. In that case people are not enough sensitive to environmental changes.

This contribution introduces an experimental study aiming to provide concrete evidence on how façade and daylight pattern geometry can affect the emotional responses triggered by a space. The study was conducted in Virtual Reality (VR) where participants were exposed to 360° scenes of an interior space with three different façade patterns. Their subjective evaluations and heart rate were recorded. The results show a statistically significant effect of façade on the perception of space, as well as the mean heart rate change. Specifically, during exposure to a façade with an irregular pattern, participants rated the space as more interesting and their mean heart rate was lower, resulting to a greater mean heart rate change compared to the resting state, providing quantifiable measures of the impact of façade characteristics on human perception and physiological behavior.

Measuring gaze allocation during scene perception typically faces a dilemma: full control over the stimulus requires comparably constrained scenarios, while realistic tasks leave the visual input hard to control. We propose to capture the full (4pi) light-field of an oce space, while participants perform typical oce tasks. Using a wearable eye-tracking device ("EyeSeeCam"), gaze, head and body orientation are measured along with subjective well-being and performance. In the present study, 52 participants performed four oce tasks ("input", "reflection", "output", "interaction"), each with three dierent tools (phone, computer, paper) under varying lighting conditions and outside views. We found that eye and head were fundamentally differently affected by view and that this dependence was modulated by task and tool, unless participants' task was related to reading. Importantly, for some tasks head movements rather than eye movements dominated gaze allocation. Since head and body movements frequently remain unaddressed in eye-tracking studies, our data highlight the importance of unconstrained settings. Beyond assessing the interaction between top-down (task-related) and bottom-up (stimulus-related) factors for deploying gaze and attention under real-world conditions, such data are inevitable for realistic models of optimal workplace lighting and thus for the well-being of an occupant's workplace.

We propose a new method for climate-based daylight modeling (CBDM) based on simulating and evaluating only the most important features. By adaptively sampling the temporal lightfield that describes daylight in buildings, our method escapes the curse of dimensionality that binds typical approaches. The method is centered around an iteratively guided sampling strategy that produces unordered sky and sun coefficient samples throughout an architectural space. This data is organized into a lightfield data structure that can be evaluated under any sky condition. Outputs include photometric quantities, visual comfort metrics, and high dynamic range images. Unlike existing CBDM methods, our approach is not limited by the rendering algorithm, material model, level of detail, or metric output. Our method is accurate and fast. As such it can serve as a general interface for any view or point-based daylighting question, including those answered by illuminance and luminance based metrics.

Due to the growing popularity of virtual reality (VR) as a tool for conducting subjective experiments, we propose a session addressing methodological concerns and good practices for the use of VR in lighting research, going further than a simple demonstration of immersive scenes. In view of the emergence of this technology as an experimental tool in lighting studies, it is important to document and establish a reference workflow, introducing potential pitfalls and suggested practices to obtain reliable data. This presentation will introduce the key elements for the design and conduction of experimental studies using VR -ranging from the creation of the immersive scenes to the particularities of collecting data when the participants are immersed in a virtual environment-, coupled with demonstrations through a virtual reality headset.

Despite numerous efforts in developing glare indices through human assessment studies, predicting visual comfort in indoor environments still poses important challenges in design. A major limitation in discomfort glare indices is that they all ignore its dependencies on view direction. In this study we adopted eye-tracking methods in a series of human assessment experiments in order to record actual visual response when experiencing discomfort glare. We set up an experiment where the view directions distributions were monitored as the participants were working in a side-lit office with three different task-supports - monitor, paper and phone - on a standardized office task sequence. The participants were allocated randomly to two groups where they were exposed to two different views from the window. The results show that the “view outside the window” is the main determinant of view direction bias whenever the participant is not focused on any cognitive or visual office task procedure.

Occupants’ visual comfort in an indoor space strongly depend on the quantity and quality of the daylight inside the space which can be altered with the type of window glazing. In this study, we compared the visual comfort perception of participants with sun in their field of view under two types of glazing: color-neutral and blue-tinted electrochromic glazing. The main experimental variables are the color and visible light transmittances of the glazing. The aim was to determine the influence of these variables on participants’ discomfort glare, view out and color perception. We found that the discomfort glare was perceived more strongly with blue-tinted glazing compared to the color-neutral glazing for a range of (low) transmittances. We also found that the colors of outdoor elements were rated non-natural in case of blue-tinted glazing compared to color-neutral glazing. The outside view was perceived more restricted in blue-tined glazing compared to color-neutral glazing even though both of them maintain view clarity.

This paper evaluates the influence of light levels (i.e., illuminance) on subjective thermal perception of people, distinguishing between thermal sensation and thermal evaluation. The goal is to investigate whether reported effects found by other studies in controlled environments can be observed in real-life contexts and to understand if results are influenced by the season. By means of a post-occupancy evaluation conducted in four buildings in Switzerland, instantaneous air temperature and illuminance measurements were collected together with occupant’s thermal perception votes during daytime in both summer and winter. Findings show that illuminance has a significant effect on the thermal perception of people, but only in terms of thermal evaluation and not of thermal sensation. In particular, results indicate that, at high temperature (above 25 °C), a less satisfying thermal evaluation is reported by people exposed to dim light (lower than 300 lux) compared to people exposed to brighter environments. We assume that this finding can be explained by thermal expectations induced by light intensity. The evaluation of data across summer and winter indicates that results are independent of the season (no interactions between illuminance, temperature and time of the year) and that the illuminance effect is accentuated depending on the season, which tends to highlight the psychological nature of thermal evaluation.

Discomfort glare metrics typically consider at least one of the two effects of discomfort glare-saturation and contrast-in their equation. The former occurs when there is an excessively bright glare source in the field of view, while the latter occurs when there is a high luminance ratio between the glare source and the adaptation level of the eye. We hypothesize that the contrast effect may dominate in low-light scenarios such as those commonly found in open-plan offices. Thus, we designed and carried out a user study in controlled laboratory conditions with 63 participants with a total of 252 scenes to investigate discomfort glare evaluations in dim daylight office environments with low adaptation levels. Our preliminary findings support our hypothesis that contrast-driven metrics predict glare responses in a more reliable way than hybrid metrics at low adaptation levels where the contrast effect dominates, which underlines the need for refining glare metrics in low brightness conditions.

In a context where lighting standards are developed based on glare indices, no study has ever investigated that these indices could be used analogously for subjects having different cultures and living in different climates. The wide variability existing between individuals’ discomfort glare perceptions suggests, however, that some of the factors influencing discomfort glare perception are still unknown, and culture might be one of them. This paper aims to determine the existence of differences between the discomfort glare perceptions of Belgians and Chileans. A field study was conducted in Chile and Belgium, for which a total of 288 measures of the lighting environments and subjective glare assessments were collected. Statistical analyses of the Belgian and Chilean datasets showed that Chileans perceive discomfort glare differently than Belgians. It is therefore hypothesised that existing discomfort glare indices might not be suited for Chilean subjects accustomed to a different type of lighting environment.

Luminance maps created on the basis of High Dynamic Range Imaging (HDRI) is a technique increasingly used to study the visual environment. But creating HDR images with commercially affordable equipment requires an extensive calibration process to ensure that luminance data and derived spatial information is correct. This paper aims to provide an overview of the necessary steps for the most commonly used HDR calibration process, based on the self-calibration routines in hdrgen/Photosphere. It also addresses commonly made mistakes and aspects requiring special attention. The described steps are: the capture of multiple exposure photographs, the response curve derivation, the HDR image generation, the vignetting and neutral density filter correction, the calibration adjustment by spot luminance measurement and the geometrical reprojection. A detailed description of the geometrical reprojection is included in this paper, since this topic has not yet been described in the literature relating to HDRI, although needed for certain lens types and glare analysis.

A well daylighted space can provide a highly satisfying visual environment. However, if that environment causes us visual discomfort, it can become such a nuisance that we, sometimes literally, turn our backs on this powerful connection to the outside world. Given this, there is enormous value in quantifying the occurrence of discomfort glare within buildings, and in glare models that may guide architects and engineers in design. With the success of climate-based modeling techniques for daylight illuminance, there is now a focus on including discomfort glare metrics in spatio-temporal evaluations. This article conducts a literature review of research focused on spatio-temporal simulations for glare assessment. Studies are reviewed according to their objectives, metrics calculated, spatial scope, temporal scope and scene variety. The goal is to document the limitations of current simulation methods, the potential to generally apply these methods, and how well these methods incorporate empirical glare research. This review finds that, due to computational constraints, there is an over-reliance on illuminance-based metrics for spatio-temporal glare assessment, even while user assessment research reinforces the importance of including contrast-based measures. To achieve an accurate zonal glare assessment, future research should focus on improving simulation efficiency and identifying ways to reduce the spatial, temporal and angular scope of the simulation, while maintaining high accuracy., SDAR Journal of Sustainable Design in Engineering of the Built Environment, 7 (1)

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. In order 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 in order 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.

This paper presents the results of an experimental study that aims to provide objective insights as to how luminance distribution in an office setting modulates our view direction (VD) in a daylit workspace while performing office tasks. Using the office-like test facility at Fraunhofer ISE (Freiburg, Germany) to create a range of controlled daylighting conditions, and a wearable mobile eye-tracker to measure eye and head orientation, we assessed VD distributions for subjects performing a standardized sequence of typical office tasks relative to two different daylight conditions: low contrast condition with no direct sunlight as compared to high contrast condition with direct sunlight coming into the room. Our results show that while the participants look more outside the window during a non-cognitive and non-visual office task, this effect is lower under the high contrast lighting conditions. Moreover, the focus of the VDs is on the task area when the participants are performing a task involving visual and cognitive activities.

Within the scope of a broader research project about visual and thermal interaction effects on human comfort and perception, the aim of this paper is to study the variation of thermal, visual and overall comfort votes of people exposed to blue and orange glazing. The study, conducted in a controlled test room and involving a total of 75 participants, is repeated at three temperature levels to investigate whether variations in comfort votes are affected by the thermal environment. Results show that participants changed their comfort votes for both thermal and overall comfort, beside the expected visual comfort, due to changes in glazing colour. Larger variations in thermal and overall comfort votes are observed in the close-to-comfortable temperature range (22 °C). Temperature-related effects can be seen for visual and thermal comfort evaluations. Overall comfort shows a positive correlation with both visual and thermal comfort.

Daylight has an undeniable value in various aspects of architectural design, ranging from energy efficiency and user comfort to our experience of space. Even though there is substantial evidence of the positive effects of daylight access on occupants, we have limited knowledge on how the façade geometry and the spatial composition of the resulting sunlight patterns in a space affect its occupants. Could a simple change of the façade change the way we perceive a space? Could it trigger different physiological reactions? This presentation investigates the intuition of architects on how façade geometry can impact occupant perception, and compares these insights with experimental findings on subjective and physiological responses to façade and sunlight pattern variations in virtual reality.

Visual comfort is important to the wellbeing of people and their productivity. However, too much light in the field of view can cause discomfort and disability glare. Under certain conditions it can even cause accidents. This paper addresses the disability glare created by veiling glare and the effect it may have of reducing the visual performance in outdoor spaces. Veiling glare is a particular case when light is reflected off a surface and causes annoyance or impairment of a task to the person in a particular view angle. Two factors that determine the nature and magnitude of veiling reflections are the specularity of the surface being viewed and the geometrical relationship between the observer, the surface and any source of high luminance. Different methods to assess disability glare exist but there is still no clear understanding on criteria to judge an outdoor scenario. A case study where reflected glare form Photovoltaics overlooking a building is of particular concern is presented.

Existing methods for glare-free daylighting design rely on analyses of physically based lighting simulations employing tools such as Radiance. The rendered image is an accumulation of luminance values from a fixed point of view, which creates a basis for luminance-based metric analysis such as discomfort glare models. A major challenge using luminance images for glare prediction analysis lies in the image processing steps for deriving different parameters of the predictive discomfort glare metrics. One of these challenges is to define and identify glary pixels and zones in the image. The glare source detection algorithms adopted in evaluation tools like evalglare, search for pixels of luminance value that are x-times larger (we call it threshold multiplier in the following) than the average luminance of a pre-defined zone, e.g. the monitor screen. As a second step, the potential glare pixels detected within a search radius (also predefined) are considered and evaluated as one glare source. The implemented default value of a threshold-multiplier and the search radius are decided intuitively and so far no validation has been made on their accuracy. The objective of the present study is to establish a sensitivity analysis on the threshold and search radius parameters. In two series of experiments we took luminance images very 30 second under different lighting conditions and with different façade systems. We also gathered the participants’ subjective assessments of the glare conditions using a Likert scale. Thereafter, we processed the images using 15 different combinations for the threshold multiplier and search radius (threshold multiplier with 5 and search radius with 3 treatment levels). The preliminary results show that there is a significant effect of threshold on all lighting conditions and an effect of search radius on lighting conditions with shading systems. But the results also show, that the choice of the ”right” detection parameters underlies also some effects, which cannot be explained so far. The consequence of this is, that further investigations are needed and as long as no clear rule exist to choose ”right” detection parameters the user of glare evaluation tools has to check the detected glare sources for each investigated situation.

There are major uncertainties in the existing glare prediction models which makes them only partially capable of predicting user responses to visual environments. The models are particularly limited when predicting glare in spaces with large non-uniform glare sources; for example a daylit office (Fisekis et al., 2003; Bellia et al., 2008; Clear, 2013; Boyce and Smet, 2014). There are also large differences in the interpersonal perception of glare. Eye colour, age and gender have been investigated but have been shown to have little to no effect on glare perception. This could be an indication that another attribute has an impact on glare perception, such as contrast sensitivity or improperly corrected eyesight (Osterhaus and Bailey, 1992; Wienold, 2009)

Luminance ratios have historically been used to assess glare. Using data from a previous experiment, this exploratory study investigates the relationship between luminance variations in the field of view (FOV), measured as luminance ratios, and glare sensation in daylit office-like settings. Correlations between glare sensation assessments and luminance ratios between task area, its immediate surround and far surround were calculated. The results indicate that there are certain definitions of contrast ratio which have better correlations with subjective assessments. The inclusion of this type of glare will enhance the existing glare models for better prediction of glare in a wider set of situations.

Office employees are exposed to a variety of environmental and contextual stimuli that might drive them to perform control actions, such as operating windows or window blinds. These actions have a significant impact on building energy use and increase uncertainty when predicting building performance. Despite the advancements in the understanding of separate fields of comfort (thermal, olfactory, visual, and acoustic), the combined effect of Indoor Environmental Quality (IEQ) factors on user perception and behaviour in real buildings merits further explorations. In this context, the eCOMBINE framework ("Interaction between energy use, COMfort, Behaviour and the INdoor Environment in office buildings") aims to create new knowledge on human-building interactions in office environments, with a dedicated focus on open plan offices. This paper provides initial results of the eCOMBINE monitoring campaign performed during a two-week period in winter (February 2020) in Switzerland. The main subjective drivers behind interactions with windows and window blinds were analysed based on self-reported actions collected with a dedicated mobile application called OBdrive, which was installed close to windows and window blinds to capture employees' motivations in real-time. The subjective feedback was supplemented with environmental data, such as operative temperature, air quality, lighting levels, and sound pressure levels. Environmental and subjective data were evaluated jointly to gain insights into the relationship between global environmental stimuli and human-building interactions. The results showed discrepancies between perceived air quality and motivation to open windows, which confirms that occupants might not always correctly interpret actual air quality. While the primary motivations for windows and blind control actions were rather logical (e.g., opening windows when it is too warm, closing blinds in case of glare), occupants' actions were often triggered by multiple motivations at a time, suggesting that a single criterion is not necessarily enough to capture occupant's action.

This poster introduces the methodology and main findings to date in Kynthia Chamilothori's PhD thesis, regarding the use of virtual reality as a substitute for experiments in the real space, and the investigation of how facade characteristics influence the perception of a daylit space.

For the application of discomfort glare metrics, a categorisation is used, dividing the metric scale into categories of perception. These categories are separated by borderline values, or so-called cut-off values. Recent literature shows that these cut-off values are lower when they are derived from field study data than those derived from laboratory study data. To investigate this further, the data from one field study and two laboratory studies was used to derive and compare cut-off values corresponding to three borderlines. The results show that the field study cut-off values were systematically lower than the laboratory study ones, implying that discomfort glare is reported at lower stimulus magnitudes in the field. Although further research is required on that topic, several hypotheses are discussed in order to explain the gap between cut-off values derived from field data and cut-off values derived from laboratory data. Recommendations for future studies are also provided.