Lumière naturelle et exigences PEB

L’introduction des règlementations sur les performances énergétiques des bâtiments a fortement complexifié le travail de l’architecte. On observe actuellement une tendance à focaliser les efforts sur la question énergétique au détriment d’autres aspects. Gardons en tête que l’optimisation d’une seule dimension – à savoir la dimension énergétique – ne garantit nullement la qualité architecturale du projet

Influence of presentation modes on visual perceptions of daylit spaces

Virtual renderings are increasingly used in the architectural design process and in lighting quality research to assess the visual appearance of indoor environments. Thanks to imaging technologies continuously in development to improve the "realism" of these images, pictures can nowadays be presented in various ways. Regrettably, to date, few studies assert that such images replicate the visual appearance perceived in actual daylit environments. The present research investigated the perceptual equivalence between actual daylit environments and images. Two types of images – photographs and virtual renderings – were studied as well as four modes of presentation – QuickTime virtual reality (QTVR) panoramas, 2D display, 3D display, and high dynamic range (HDR) display. Eight groups of 40 students viewed four daylit corridors and filled in a questionnaire about the appearance of lighting and space elaborated for the study. The corridors were presented in several ways: a first group of participants visited the actual rooms while the other groups visualized, in a lab context, their reproduction in sketches, photographs or virtual renderings. This research provides some proofs that images can reasonably be used as a surrogate for the real world when studying the appearance of lighting (characterized by the perceived brightness, coloration, contrast, distribution, directivity and glare). On the other hand, the study suggests that images poorly reproduce the appearance of space (pleasantness and enclosedness were studied). As a result of the research, we determined precisely the media to use for studying each dimension characterizing the appearance of lighting and space.Afin d’évaluer les qualités spatiales et lumineuses des espaces qu’ils conçoivent, les architectes ont régulièrement recours aux rendus virtuels. Dans le domaine de la recherche en éclairage également, l’utilisation de ce type d’image est de plus en plus répandue. Pourtant, tandis que de nombreuses technologies de l’image sont développées afin d’encore accroître leur réalisme, peu de travaux ont démontré que celles-ci reproduisent fidèlement les perceptions visuelles ressenties dans les environnements réels. A l'aide d'enquêtes par questionnaire menées auprès de 320 étudiants universitaires, l'équivalence perceptuelle entre des environnements réels éclairés naturellement et leur reproduction en image a été investiguée. Deux types d'images – des photographies et des rendus virtuels Radiance - ont été étudiés ainsi que quatre modes de présentation – l’image 2D traditionnelle, la panoramique QTVR, un écran 3D et un écran HDR en développement (écran permettant d’afficher une large gamme de luminosités). Les résultats obtenus indiquent que la plupart de ces images peuvent être utilisées comme substitut du monde réel lorsqu’on étudie l'apparence de l'éclairage (caractérisée par les dimensions suivantes : luminosité, coloration, contraste, distribution, directivité et éblouissement). Par contre, l'étude révèle que ces images reproduisent peu fidèlement l'apparence de l’espace (les caractères agréable et enclos ont été étudiés). A l’issue de la recherche, les types d’image et les modes de présentation à favoriser pour l’étude de chacune des dimensions caractérisant l’apparence de l’éclairage et de l’espace ont été précisément déterminés.(FSA - Sciences de l'ingénieur) -- UCL, 201

A color graphic informing on the impact of electric lighting and coated glazing in complex architectural scenes

The present work proposes a graphical indicator that provides descriptive information about the color content of architectural environments, and shows color shifts due to illuminant or glazing changes. This color graphic is in accord with representations recently developed in electric lighting to provide information on color rendering. Its originality lies in (1) including contextualization, (2) dividing the color space based on color naming, and (3) giving the user the opportunity to compare scenes with different correlated color temperatures. After describing the development steps of the color graphic, two case studies and three validation experiments are presented. While the application of the graphic highlights its interest in a building design process, the validation experiments identified potential improvements

Assessing daylight luminance values and daylight glare probability in scale models

This paper presents a research about the possibility to use a scale model of a room to assess the luminances in the visual field of the room's user, and consequently its risk of glare. Measurements of luminance values by the HDR technique were done simultaneously in a room and its 1/6 scale model, with identical measurement material. The room was lit by a lateral window either unprotected from direct sun radiation, or fitted with a white or black screen. Measurements show that luminance values obtained in the scale model are overestimated and that the relative differences between values in the scale model and in the mock-up vary between 10 and 50% for the situation without shading device, between 45 and 80% for the window equipped with the white screen and between 0 and 45% with the black screen. Yet, the evolution of luminances is very similar for both rooms, and a high level of correlation is observed between glare index DGP values calculated on these respective luminance values, despite a very slight over-evaluation of the DGP in the scale model. In conclusion, for the situation tested, the DGP can be evaluated using a 1:6 scale model, under the condition of very accurately respecting the geometry and photometric data of the studied room walls. It is also very important to position the scale model in a way to obtain a view on the outside as similar as possible to the one obtained from the studied room

Atmosphère ! Atmosphère !

Dans le cadre de leurs travaux respectifs menés à la Faculté d'architecture, d'ingénierie architecturale, d'urbanisme (LOCI ) de l’UCL, les deux chercheurs se rencontrent autour de la notion d’atmosphère et de la capacité de l’image à en rendre compte. Leurs échanges visent à mieux définir le terme atmosphère car, si la notion est évocatrice en architecture, elle s’avère en second lieu peu définie

Application of High-Dynamic Range Imaging Techniques in Architecture: A Step toward High-Quality Daylit Interiors?

High dynamic range (HDR) imaging techniques are nowadays widely used in building research to capture luminances in the occupant field of view and investigate visual discomfort. This photographic technique also makes it possible to map sky luminances. Such images can be used for illuminating virtual scenes; the technique is called image-based lighting (IBL). This paper presents a work investigating IBL in a lighting quality research context for accelerating the development of appearance-driven performance indicators. Simulations were carried out using Radiance software. The ability of IBL to accurately predict indoor luminances is discussed by comparison with luminances from HDR photographs and luminances predicted by simulation in modeling the sky in several other more traditional ways. The present study confirms previous observations that IBL leads to similar luminance values than far less laborious simulations in which the sky is modeled based on outdoor illuminance measurements. IBL and these last methods minimize differences with HDR photographs in comparison to sky modeling not based on outdoor measurements

Calibration of high dynamic range images for applied color and lighting research

The main objective of this work is to determine the most appropriate high dynamic range picture calibration procedure for measuring luminance and color, in the context of architecture. Three professional digital single-lens reflex cameras fitted with fisheye lenses were tested. Photometric and colorimetric accuracy was assessed in comparison with spectroradiometer measurements of 57 color samples (Macbeth chart and additional Munsell samples). The results demonstrate that using a calibration model specific to the camera–lens association rather than the standardized RGB to XYZ color transform matrix is necessary to achieve an acceptable colorimetric accuracy. Moreover, using a specific color transform matrix reduces the error in luminance, especially for colorful elements. The study also shows the opportunity to share the same color transform matrix between similar photographic materials (same brand and model). Finally, among the three tested devices, one camera–lens association has higher performance and produces better quality QuickTime Virtual Reality panoramas

CIE 2017 color fidelity index Rf: a better index to predict perceived color difference?

The CIE General Color Rendering Index Ra is currently widely and internationally used to assess the ability of white light sources to render colors. But over the past decades, there has been increasing evidence of its limitations. As a result of several years of scientific work, the Commission Internationale de l’Eclairage (CIE) published in April 2017 an updated calculation method. To reduce misinterpretation by users and make a clear distinction with the other aspects of color quality, the color rendering index was renamed color fidelity index (CIE-Rf). Before proposing this index as a new international standard for color fidelity prediction, there is a need for validation. This paper presents a psychophysical experiment designed to address this aim. Twelve observers evaluated color differences of 16 color samples under eight pairs of light sources. 3000K and 4000K light-emitting diodes and fluorescent sources with CIE-Rf values ranging from 64 to 94 were investigated. Results show that the prediction of color differences is significantly better in CAM02-UCS color space than in CIE U∗V∗W∗ or CIELAB, whatever the color matching functions. A high correlation was found between perceived color differences and CIE-Rf. This psychophysical experiment did not make it possible to detect significant differences with the other tested color fidelity indices (CIE-Ra, CQS-Qf, CRI2012, CRI-CAM02UCS, and IES-Rf). However, there are some signs of an improvement of the prediction by CIE-Rf in comparison to CIE-Ra. To increase, in further works, the chance to detect potential significant differences between color fidelity indices, some modifications of the experimental protocols are suggested