A new daylight glare evaluation method: Introduction of the monitoring protocol and calculation method

Ergonomic design of workplaces requires a proper method for predicting glare to promote visual comfort. Only a few formulae have been proposed for discomfort glare of daylight origin, and they are inadequate to predict glare sensation in real daylight situations. No standard monitoring procedure is available to establish a basis for glare evaluation on a comparative basis under real sky conditions. This paper introduces a new glare evaluation method consisting of a standard monitoring protocol and formulae for window luminance, adaptation luminance and exterior luminance, and formulae for the solid angle, the modified solid angle and the configuration factor of the window. The glare evaluation procedure was developed with the hope that architects and lighting designers would adopt it as an easy and reliable method for evaluating discomfort glare sensation from daylighting. The method has yielded in real measurements and computer simulations sensible and consistent glare values. The results of the experiments, however, are not presented here in their entirety because of the large size of that part. The future work, which is an ongoing research, is to create the use of scientific-knowledge computational tools in the later stages of design in an effort to provide optimum choices of daylighting design with respect to light level and glare using the new glare algorithm.     

Evaluation methods and development of a new glare prediction model for daylight environments with the use of CCD cameras

Daylighting and the impact of daylighting strategies on the visual environment continue to be a vital issue for building occupants due to visual comfort and user acceptance of luminous indoor environments. Some of the critical factors affecting the level of visual comfort and quality in daylit office spaces include glare, window luminances, and luminance ratios within the field of view. One of the goals of this study was to provide new insight into the impact of luminance distributions on glare. The luminance distribution within the field of view was recorded using CCD camera-based luminance mapping technology. The technology provides a great potential for improved understandings of the relation between measured lighting conditions and user response. With the development of the RADIANCE based evaluation tool “evalglare”, it became possible to analyse glare according to a number of daylight glare prediction models as well as contrast ratios in various daylit situations (workplace, VDU). User assessments at two locations (Copenhagen, Freiburg) with more than 70 subjects under various daylighting conditions were performed in order to assess existing glare models and to provide a reliable database for the development of a new glare prediction model. The comparison of the results of the user assessments with existing models clearly shows the great potential for improving glare prediction models. For the window luminance a squared correlation factor of only 0.12 and for the daylight glare index (DGI) of 0.56 were found. Due to the low predictive power of existing glare prediction models a new index, daylight glare probability (DGP), was developed and is presented in this paper. DGP is a function of the vertical eye illuminance as well as on the glare source luminance, its solid angle and its position index. The DGP showed a very strong correlation (squared correlation factor of 0.94) with the user's response regarding glare perception.     

Effect of switchable glazing on discomfort glare from windows

In this paper we report the results of experimental tests carried out to study the effect of electrochromic (EC)-glazing on discomfort glare from windows. The research is performed by a small scale test-cell equipped with a small area double glazing unit (DGU) where one pane consists of an EC device with a visible transmittance τ_v ranging from about 7 to 70% and the other of an ordinary clear float glass (τ_v ∼ 90%), the overall DGU transmittance dynamic range resulting about 4–58%. The performance of the device is investigated under real sky conditions as a function of time, solar radiation intensity, test-cell orientation and switching strategies (static and dynamic). The evaluation methods adopted for assessing the discomfort glare degree are the “New Daylight Glare Index” (DGI_N) and the “Glare Subjective Rating” (SR). Results deriving from application of these two methods are compatible and show that for south facing windows and under the involved climatic conditions EC-glazing can be very effective in reducing discomfort glare caused by high window brightness originating from diffuse skylight. This glare reduction can be realized without compromising much of the available daylight so without necessarily increasing the need for artificial lighting and, at the same time, preserving an unobstructed outside view. Occurrence of glare effects from west (or east) facing windows is more difficult to be controlled due to the lower sun angles which entail the use of EC devices switchable to very low transmittance states (τ_v < 7%) and/or integration of traditional sun protection devices. This would probably compromise indoor daylight availability (and potential energy savings associated to reduced use of artificial lighting) as well as exterior view although the positive effect of the EC-glazing could be a substantial reduction of the frequency of use of these additional shading systems.     

A dynamic sky recognition method for use in energy efficient lighting design based on CIE standard general skies

This paper innovatively proposes an “active green lighting model” for control and optimization of building luminous environment. It is expected to optimize the utilization of daylight dynamically in energy efficient lighting design from the viewpoint of intelligent control. As one primary work of implementing the overall model, the luminance distribution of CIE standard general Skies is addressed, and a dynamic sky recognition method for utilization optimization of daylight is proposed based on swarm intelligence. The experiment results of instance field data show the proposed intelligent sky recognition method is feasible and effective.     

Comparison between lighting performance of a virtual natural lighting solutions prototype and a real window based on computer simulation

This article discusses the measurement and simulation of a first generation prototype of Virtual Natural Lighting Solutions (VNLS), which are systems that can artificially provide natural lighting as well as a realistic outside view, with properties comparable to those of real windows and skylights. Examples of employing Radiance as a simulation tool to predict the lighting performance of such solutions are shown, for a particular case study of a VNLS prototype displaying variations of a simplified view of overcast, clear, and partly cloudy skies. Measurement and simulation were conducted to evaluate the illuminance distribution on workplane level. The key point of this study is to show that simulations can be used to compare an actual VNLS prototype with a hypothetical real window under the same sky scenes, which was physically not possible, since the test room was not located at the building׳s façade. It is found that the investigated prototype yields a less rapidly drop illuminance distribution and a larger average illuminance than the corresponding real window, under the overcast (52 lx compared to 28 lx) and partly cloudy (102 lx compared to 80 lx) sky scenes. Under the clear sky scene, the real window yields a larger average illuminance (97 lx) compared to the prototype (71 lx), due to the influence of direct sunlight.     

Effects of real-time simulation feedback on design for visual comfort

Building performance simulations and models of human visual comfort allow us to predict daylight-caused glare using digital building models and climate data. Unfortunately, the simulation tools currently available cannot produce results fast enough for interactive use during design ideation. We developed software with the ability to predict visual discomfort in real time. However, we know little about how users react to simulation feedback presented in real time. In our study, 40 subjects with backgrounds in building design and technology completed two shading design exercises to balance glare reduction and annual daylight availability in two open office arrangements using two simulation tools with differing system response times. Subjects with access to real-time simulation feedback tested more design options, reported higher confidence in design performance and increased satisfaction with the design task, and produced better-performing final designs with respect to spatial daylight autonomy and enhanced simplified daylight glare probability.     

A Regionally-Applicable model of union growth: Comment

This paper criticizes the approach used by M. Snowbarger in “A Regionally-Applicable Model for the Study of the Growth of Organized Labor,” The Annals of Regional Science, February, 1974. It is argued that the division of union membership change into “product-market” and “factor-market” effects has serious conceptual flaws, as well as using a special case of decomposition of change in a weighted aggregate, so that unambiguous partitioning of total change is impossible.     

Useful daylight illuminances: A replacement for daylight factors

This paper describes the application of a new paradigm, called useful daylight illuminance (UDI), to assess daylight in buildings. The UDI paradigm is designed to aid the interpretation of climate-based analyses of daylight illuminance levels that are founded on hourly meteorological data for a period of a full year. Unlike the conventional daylight factor approach, a climate-based analysis employs realistic, time-varying sky and sun conditions and predicts hourly levels of absolute daylight illuminance. The conventional approach produces a single number – the daylight factor as a percentage – for each evaluation point in the space. In contrast, a climate-based analysis results in an illuminance prediction for every daylight hour of the year for each point considered. The UDI paradigm offers a way to reduce the voluminous time-series data to a form that is of comparative interpretative simplicity to the daylight factor method, but which nevertheless preserves a great deal of the significant information content of the illuminance time-series. The UDI paradigm informs not only on useful levels of daylight illuminance, but also on the propensity for excessive levels of daylight that are associated with occupant discomfort and unwanted solar gain. In a conventional analysis of daylight provision and solar penetration, the two phenomena are assessed independently using methods that are idealised (daylight factor) and qualitative (shadow patterns). The UDI paradigm offers a simple methodology whereby daylight provision and levels of solar exposure are quantified using a single evaluative schema. Thus, it is also well-suited for teaching purposes. Application of the UDI paradigm is demonstrated using an analysis of design variants for a deep-plan building with a light-well. Comparison is made with the conventional daylight factor approach, the LEED daylight credit and measures of daylight autonomy.     

A first approach to discomfort glare in the presence of non-uniform luminance

This study aims to elucidate the difference in glare sensation between uniform and non-uniform glare sources. In the experiment, the degree of discomfort glare is examined using simulated windows of uniform and non-uniform surface luminance. The window plane is divided into two parts, the upper and lower surfaces, and the luminance and solid angle of each surface are set differently. The upper and lower parts are assumed to be the sky and obstacle, respectively. Two conclusions follow from this study. First, the degree of discomfort glare for the uniform window is higher than it is for the non-uniform window, when the luminance of the uniform window is the same as the average luminance of the non-uniform window. Therefore, the discomfort glare sensation of the non-uniform window is different from that of the uniform window. Second, the glare source in the non-uniform window is restricted by luminance and originates from parts ranging from the highest level of luminance down to a level that is 61% of the highest level of luminance. These results may be useful for selecting the glare source in a window with a non-uniform luminance distribution.     

An analysis of climatic parameters and sky condition classification

In modelling solar radiation, of the required data daylight illuminance, luminous efficacy, radiance and luminance sky distributions, are always analysed under various sky types. Sky conditions are frequently categorised into overcast, partly cloudy and clear using some common climatic data including cloud cover (CLD), sunshine hour (SH) and solar radiation. This paper presents the study of these climatic parameters and their applications in the classification of sky condition. Frequency of occurrence and cumulative frequency distribution of each sky indicator have been established to interpret the prevailing sky conditions in Hong Kong. Special features on defining the sky clearness are highlighted and the implications for energy-efficient building designs are discussed.     

A simplified procedure for determining indoor daylight illuminance using daylight coefficient concept

The first step in evaluating the visual performance and energy efficiency provided by daylight requires an accurate estimation of the amount of daylight entering a building. The actual daylight illuminance of a room is mainly influenced by the luminance levels and patterns of the sky in the direction of view of the window at that time. The daylight coefficient concept, which considers the changes in the luminance of the sky elements, offers a more effective way of computing indoor daylight illuminances. Recently, Kittler et al. have proposed a new range of 15 standard sky luminance distributions including the CIE (International Commission on Illumination) standard clear sky. Lately, these 15 sky luminance models have been adopted as the CIE Standard General Skies. This paper presents a graphical method to calculate interior illuminance for the CIE standard clear sky using the daylight coefficient approach. The simplified techniques in the form of a nomograph and Waldram diagram were established and described. The performance of the proposed approach was evaluated against the results obtained by an independent calculation approach and a computer simulation program. It was shown that the daylight illuminances estimated by our graphical tool were in reasonably good agreement with those produced from the other two methods. The findings provide building professionals and students a reliable and simple alternative that incorporates the daylight coefficient concept to estimate the interior daylight illuminance and assess daylighting performance.     

The daylighting dashboard – A simulation-based design analysis for daylit spaces

This paper presents a vision of how state-of-the-art computer-based analysis techniques can be effectively used during the design of daylit spaces. Following a review of recent advances in dynamic daylight computation capabilities, climate-based daylighting metrics, occupant behavior and glare analysis, a fully integrated design analysis method is introduced that simultaneously considers annual daylight availability, visual comfort and energy use: Annual daylight glare probability profiles are combined with an occupant behavior model in order to determine annual shading profiles and visual comfort conditions throughout a space. The shading profiles are then used to calculate daylight autonomy plots, energy loads, operational energy costs and green house gas emissions. The paper then shows how simulation results for a sidelit space can be visually presented to simulation non-experts using the concept of a daylighting dashboard. The paper ends with a discussion of how the daylighting dashboard could be practically implemented using technologies that are available today.     

场景作为建筑空间的一种所指

建筑的空间基本上体现为公共性的和基础性的,特别是受形态意识的操控,在意繁复的视觉系统大于使用的内容,形式样态实际上变为脱离于本原的解构。然而,场景是空间中的派生,富有清晰、稳定的规则和适当行为的指令,并呈现为文化的变量关系。因此,文章以空间转换为场景来理解,认为场景构成在于"布置",发展和满足人们行为及交流的多样化,进而印证为空间是"无",场景是"有"的概念。     

A design tool for predicting the performances of light pipes

Light pipes are simple means of directing daylight (diffuse and direct light) into interior spaces. Previous work by the authors described the initial work on a luminous flux and illuminance predictive model for straight light pipes, using a basic equation for illuminance distribution as a function of horizontal distance. Further work has now produced a model that uses the cosine law of illuminance to describe the distribution of light from the light pipe diffuser as well as takes into account pipe elbow pieces or bends. The resulting illuminance model can be described as a quartic cosine model. By producing a “luxplot” prediction for any given light pipe application, it is possible to maximise the potential of these daylight providers and design their configuration to suit any given need. As part of this study, wide-ranging illuminance and luminous flux data were collected both for the formulation of this model (as the formula is semi-empirical) and its validation.     

A comparison of luminous efficacy models based on data from Vienna, Austria

To support building design in view of daylight quality, computational (simulation) tools can provide effective support. To perform detailed daylight analysis via simulation, appropriate sky models are needed. In the past, various sky luminance distribution models have been developed. Such models, however, require illuminance data for the relevant location. As measured external illuminance levels are not available for many locations, the more widely available irradiance measurements can be translated, using proper luminance efficacy functions, into illuminance values. The present paper compares five global luminous efficacy models based on a database of measured illuminance and irradiance data from Vienna, Austria. These models typically involve mathematical formulations with multiple coefficients, whose values are derived for a specific location. The results suggest that these models performed rather poorly, once tested against Vienna data. However, the models’ performance improved significantly, once the respective coefficients were modified (calibrated) using the Viennese database.     

Design and assessment of an anidolic light-duct

The system presented here, called Anidolic Ceiling, was developed to show the viability of intensive use of daylight by overcast outdoor conditions in nonresidential buildings. This device consists of a light-duct that is integrated in a suspended ceiling and leads midway into the office. Anidolic (nonimaging optics) elements are placed on either end of the duct, on the outside to collect light rays from the sky and on the inside to control the direction of the emitted light. The present paper describes the system design, as well as an experimental assessment of its daylighting performance in a comparison of a prototype and a full-size conventional facade, for a 6.6-m deep room. Measurements by overcast sky have established that the daylight factor on the work plane 5 m from the window is more than doubled. In addition, a monitoring campaign has shown that 30% of the energy for lighting can be saved. The system was also assessed with regard to the user. Visual comfort measurements (Laboratoire d'Ergonomie de la Vision's (LEV) method) were carried out showing that for both clear and overcast outdoor conditions, the visual environment quality is objectively improved at the rear working place. Furthermore, 33 people tested both rooms one after the other. They were submitted to a series of visual acuity tests on printed paper and on a computer screen and had to fill in a questionnaire. A comparative study showed that the personal appreciation of the luminous environment is better in the room with an Anidolic Ceiling, with a significant reduction of reading errors both on paper and on the screen.     

Behavior of luminous zones appearing on plumes of large-scale pool fires of kerosene

In order to understand characteristics of large pool fires, behavior of intermittent luminous zones appearing on the smoky plumes has been analyzed using a recently developed image processing technique. The images of large pool fires analyzed in this study are of 30 and 50-m diameter pool fires of kerosene recorded on videotapes at the large-scale experiments performed in Japan, 1981. The results indicate that the probability of a luminous zone appearing is the maximum on the central point of the average plume width and at a distance from its base, and decreases with the distance from the maximum point. It can be inferred that the luminous zone on the smoky plume of a pool fire likely appears at its concave boundary (in a side view). It ascends at an almost constant velocity while changing it's area at the same frequency as that of the “breathing”.     

Daylighting of buildings in a hot climate

The utilization of daylight in buildings can save energy and reduce pollution. Furthermore, daylight is preferred by most people because of the spectral composition and the contact with the outside world which is provided by windows. On the other hand, glare and heat gains during the hot season should be avoided. This can be achieved only by careful control of the admitted solar radiation. As a rule, direct sunlight inside the building should be avoided, at least during the hot season. An advanced computer package, based on accurate analytical equations for the calculation of daylight, has been developed for overcast as well as clear sky conditions. The package is meant to be readily usable by non-specialists in computer programming. Complicated configurations of interiors, with any given wall thickness, having rectangular or oblique walls and partitions, can be computed. Furthermore, the same package is extended to deal with the total thermal balance of the building.     

Daylighting simulation in the DOE-2 building energy analysis program

A daylighting calculation has been intergrated grated into the DOE-2 building energy analysis computer program. Users can, for the first time in a widely-accepted, publicly-available program, determine the impact of daylight utilization on heating and cooling loads, energy use, energy cost, and peak electrical demand. We describe the algorithms which simulate hourly-varying interior illuminance, management of windows for sun and glare control, and the operation of electric lighting control systems. Sample DOE-2 daylighting output reports are presented and results of program validation against scale model illuminance measurements using the Lawrence Berkeley Laboratory sky simulator are discussed.