Application of a spectral sky in Radiance for daylighting calculations including non-image-forming light effects

Daylight is dynamic and rich in the blue part of the spectrum. To date, the spectral composition of daylight is ignored in sky models used in Radiance. Spectral sky composition is particularly important when non-image-forming (NIF) light effects are concerned, since the action spectrum for these effects differs from that of the image-forming (IF) effects as it is shifted towards the blue. Recently, Stock has implemented the analytic spectral sky model proposed by Preetham and colleagues approximating daylight’s full spectrum in Radiance for a clear sky condition (Preetham, Shirley, & Smits, 1999; Stock, n.d.). However, this spectral sky has not been used in Radiance for irradiance simulations. This study is focusing on the accuracy of daylight simulations in Radiance implementing the spectral sky model. The aim is to investigate the usability of the spectral sky model in simulations for both IF and NIF calculations. Simulations are performed using the CIE clear and the spectral sky model for two locations (Eindhoven, the Netherlands and Utah, USA). Spectral data (in RGB bands) throughout working hours were estimated and compared for different sun positions (March 15th, June 15th, and December 15th). For the Eindhoven location, simulated data are compared with small-scale measurements. To assess the NIF effects of daylight using simulated data the method suggested by (Geisler-Moroder & Dür, n.d.) is implemented. The findings show that, when the two sky models are compared, results are comparable for the higher sun angles, but significantly different for low angles

Modelling and simulation of virtual natural lighting solutions with complex views

In situations where daylight is insufficiently available, Virtual Natural Lighting Solutions (VNLS) can be promising to turn currently unused floor space into spaces with enough daylight qualities. This article introduces VNLS models with complex image scenes pasted on a transparent glass surface in front of arrays of small, directional white light sources. The objectives are twofold; the first one is to understand the effect of changing input variables, i.e. beam angle, total luminous flux of the 'sky' elements, and image scene itself; on the lighting performance of a reference office space. The second objective is to compare two techniques of modelling the view, i.e. transmissive and emissive approaches, using Radiance. Sensitivity analysis of the simulation results show that under every image scene, the total luminous flux of the 'sky' element is largely influential to the space availability, whereas the beam angle of the 'sky' element is largely influential to the other output variables, including discomfort glare. The findings lead to a suggestion of preferred elements in the image scene, to ensure large space availability and uniformity. The transmissive approach generally generates smaller values of space availability, and largely depends on the view elements of the image scene. In turn, the average probability of discomfort glare using the transmissive approach is smaller than that using the emissive approach

Simulation of virtual natural lighting solutions with a simplified view

Daylight is limited in time and space. In situations where daylight is insufficiently available, virtual natural lighting solutions (VNLS), which are systems that artificially provide lighting and view comparable to those of real windows and skylights, can be promising. VNLS can turn currently unused floor space into space with daylight qualities. The space-gaining potential of VNLS in buildings can be predicted using computational building performance simulation. This paper describes the approach of modelling VNLS with a simplified view, using the Radiance tool to evaluate the lighting performance in a reference office. The VNLS are modelled as arrays of small light sources resembling the sky, the horizon and the ground. The simulation results show that VNLS with wide beam angles generally offer a better uniformity and a larger percentage of sufficiently lit workplane area compared to those obtained with real windows under overcast sky conditions, while the discomfort glare remains comparable to that received from real windows

A multidirectional spectral measurement method and instrument to investigate non-image-forming effects of light

\u3cp\u3eLight directionality, spectrum and relevant radiometric or photometric quantity are believed to be essential factors influencing the magnitude of non-image-forming effects. In this paper, a measurement method and an instrument (the multidirectional spectroradiometer - MuS) is proposed, which considers different light incidents and spectra simultaneously, therefore enabling the measurement of light characteristics relevant for non-image-forming effects. The MuS consists of four spectroradiometers measuring in different directions. Four spectrometers using optical fibers were configured to measure the spectral irradiance within a wavelength range from 200-1100 nm with ∼5.7 nm pixel resolution. Application of the MuS facilitates a better understanding of the non-image-forming light characteristics of space. The MuS was tested with stable electric lighting as well as dynamic daylight conditions and proved reliable to perform continuous spectral measurements for different directions simultaneously. Results of the test measurements in dynamic daylight conditions show differences in the spectral distribution and measured irradiance of up to 30 times in different directions.\u3c/p\u3

Considerations on design optimization criteria for windows providing low energy consumption and high visual comfort

Apparent window size contradictions arise when optimizing simultaneously for low energy (small sizes) and visual comfort (large sizes). Diverse multi-objective optimization methods exist, but basic questions must be solved beforehand such as choosing appropriate evaluation measures. This work aims to determine the suitability of combined optimization criteria on window sizing procedures for low energy consumption with high visual comfort and performance. The paper showcases diverse measures available to valorise energy consumption and visual aspects. A series of energy and visual criteria were selected, defining acceptance thresholds for dynamic evaluations. Whole-building computer simulations were performed on a standardized office located in a temperate climate. Discrete window-to-wall ratio variations were studied to demonstrate how these criteria affect the solution space. Results were classified using a graphical optimization method, obtaining a solution space satisfying both energy and visual requirements. Most project expectations can be met within the range of sizes. However, unprotected windows barely meet acceptance criteria, needing additional control devices. Applying various related criteria with adequate values increases the diversity of acceptable solutions but too many limits it. Clear objectives and acceptance ranges have to be conceptualized in order to translate them into decisions. This becomes important when involving team design

Effect of different design parameters on the visual and non-visual assessment criteria in office spaces

Light entering the human eye does not only enable the performance of visual tasks, but also influences the health and well-being of humans via non-visual effects. A substantial amount of people in the Western society spends the majority of their work time indoors. Well-designed lighting positively impacts the visual comfort and well-being of people working in offices. Current standards for office lighting design are solely based on enabling the visual tasks via recommendations for photometric quantities such as the maintained illuminance on the task and surrounding areas and/or the glare limitation. The luminous radiation that contributes to the health related non-visual effects is not addressed in these recommendations at all. It is therefore essential to include the impact of effective luminous radiation in the lighting design process. This paper discusses the necessary distinction between photometric quantities on one side and effective luminous radiation on the other side. It investigates the effect of design parameters such as 'window size', 'exterior ground plane color and luminous reflectance' on the visual and non-visual effects for different view directions. Simulations have been conducted for the IEA Task 27 reference office using the light software tool Radiance The findings show reverse influence of the exterior ground plane color and luminous reflectance on the visual and non-visual effects of light. While the exterior ground plane luminous reflectance plays an important role on the visual evaluations, its color is the most influential design parameter for the non-visual evaluations. For the optimal health related non-visual effects of light, findings suggest using bluish exterior ground plane and placing the work plane facing the window