In the field of lighting, luminance maps are often used to evaluate point-in-time lighting scenes from the occupant's vantage point. High Dynamic Range (HDR) photography can be used to generate such luminance maps. The aim of this tutorial is to present a comprehensive overview of a step-by-step procedure to generate a 180°luminance map of a daylit scene from a sequence of multiple exposures with semiprofessional equipment and the Radiance suite of programs. The procedure consists in capturing a sequence of multiple exposures of the visual scene; selecting the useful exposures; merging the exposures to generate the HDR image by using the predefined camera response function; nullifying the exposure value; resizing and cropping the HDR image by using the predefined fisheye view coordinates; adjusting the projection of the HDR image by using the predefined distortion function; correcting the vignetting of the HDR image by using the predefined vignetting curves; correcting the alterations of the HDR image due to the Neutral Density (ND) filter if one was used, by using the predefined ND correction function; adjusting the photometry of the HDR image by using the measured spot luminance value; editing the HDR image header by using the predefined projection type and real viewing angle; and checking the validity of the HDR image by using the measured vertical illuminance, and, if needed, the predefined luminous range. To conclude, an analysis of errors is made and attention points to adapt the procedure for electric or circadian lighting studies are discussed.

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 UVW 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.

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Manuscript Code: 0446 Date of reception/acceptation: 01sep2014/01dec2014Resumen La efectividad y precisión de un estudio de iluminación natural depende de conocer las condiciones de clima y la luz disponibles en un lugar, para así evaluar la iluminancia obtenida durante el proceso proyectual. Se presentan las metodologías aplicadas de una investigación realizada cuyo objetivo fue conocer y entregar datos realistas de la distribución espacial de los cielos, para así construir las bases para futuros estudios de iluminación en Chile. Se inicia con una revisión de las métricas para cuantificar la luz natural; posteriormente se presenta la metodología utilizada para levantar la información de frecuencias mes a mes en cuatro tipos de cielos CIE estándar a partir de archivos meteorológicos. Finalmente, se expone el método de fotografías de alto rango dinámico (High Dynamic Range-HDR) aplicado para conocer la distribución espacial de los cielos de seis ciudades de Chile. Se concluye que conocer los cielos CIE estándar posibilita focalizar los estudios de iluminación natural para cielos predeterminados, realizando un diseño y análisis para los cielos más frecuentes. Así mismo, el método aplicado para caracterizar la distribución espacial de los cielos debe ser calibrado para cada localidad de estudio.Palabras claves: Luz Natural, modelos de cielo CIE, distribución de iluminancia del cielo, fotografía de alto rango dinámico, captura del cielo AbstractThe effectiveness and accuracy of a daylighting study relies on knowing the climate and light conditions available at a given place, to then evaluate the illuminance obtained during the project development process. This paper presents the methodologies of a research process, whose objective is providing realistic data to establish the foundations for future lighting studies in Chile. It starts with the revision of the metrics used to quantify daylight; later, the methodology used to collate the monthly frequencies on four types of standard CIE skies, starting from climate files, is presented. Finally, both the methodology and the results obtained are presented to measure and characterize the real skies, as well as the High Dynamic Range photographs (HDR) and, as complement of this information, the illuminances measurements of the sky dome to define the types of skies of six Chilean cities. From the study applied, it is possible to conclude that knowing the standard CIE skies of a place allows us to adjust and focus the daylighting study for predetermined and predominant skies. It is just as important to mention that the measuring techniques for the skies must be adjusted and calibrated for each studied location.

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.

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.

High Dynamic Range (HDR) imaging techniques are frequently used in lighting research for measuring luminance. The main objective of this work was to determine to what extent they can also be used for measuring colours. Three professional digital single-lens reflex cameras fitted with fisheye lenses were used for taking HDR pictures. The scene, containing a Macbeth chart and additional Munsell samples, was lit by a LED equi-energy spectrum source. The set of colour samples had first been characterized using a spectrophotometer. This article presents and compares two calibration methods, a conventional and an alternative one. It was demonstrated that the second method is necessary to achieve an acceptable colorimetric accuracy for lighting design of interior environments, and that it improves the luminance accuracy. The study also shows that one of the studied devices has higher accuracy performances.