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Lighting + Space: Calculating the Results
Published in Michael Stiller, Quality Lighting for High Performance Buildings, 2020
A common calculation method used by many of the currently available lighting design software programs to create renderings is called radiosity. With this method, light is depicted in a very natural way, with soft shadows and gradient highlights. An example of a rendering generated with radiosity is shown in Figure 6-6. In a radiosity calculation the light from a source, be it a lighting fixture or the sun streaming into an open window, reflects from surface to surface until it is fully absorbed, illuminating the room along the way, just as it would in the real world. Radiosity calculations can be used to show the illuminance we can expect to achieve in a specific room at a specific place and time, taking into account the contribution of the electric lighting specified and the daylight that will be present, to give us a complete picture of the interior lit environment. Many of these software programs, which are for the most part easily run with the resources of today’s personal computers, can also produce daylight studies to show the actual path of direct sunlight into a specific building or interior space. This kind of study can be of great assistance to architects and designers in developing appropriate window overhangs and light shelves, to bring more effective daylight into an environment while controlling glare. This can be an integral part of the practice of daylighting, which we will examine later.
Daylight performance predictions
Published in Jan L.M. Hensen, Roberto Lamberts, Building Performance Simulation for Design and Operation, 2019
Radiosity was originally developed to solve problems involving radiative heat transfer between surfaces based on form factors. Since the 1980s, radiosity has also been applied in computer graphics to calculate illuminance levels due to electric lighting or daylight. A form factor defines the fraction of radiative energy leaving a given surface to the energy that directly arrives at a second surface. In radiosity, each surface is treated as a perfectly diffuse reflector with a constant luminance so that the radiation exchange between two surfaces can be described by a single number, which depends on the reflective properties of the surfaces as well as the overall scene geometry. To calculate the indoor luminance distribution in a room due to daylight, the incoming luminous flux through all non-opaque parts of the building envelope is set equal to the available flux within the building. This assumption defines a set of equations that uniquely determine the luminances of all considered surfaces. The basic radiosity approach can be coupled with a finite element approach, which detects regions with a large luminance gradient between neighboring surface patches and subsequently subdivides the affected surfaces into sub-surfaces. A detailed description of radiosity methods can be found, for example, in Cohen and Wallace (1993).
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Published in Phillip A. Laplante, Dictionary of Computer Science, Engineering, and Technology, 2017
radiosity an image rendering algorithm that allows diffuse and mutual illumination effects by evaluating the radiation of light from light sources and reradiation among surfaces. Radiosity calculations determine the steady state in the radiative transport of light around a closed volume. Essentially, the illumination leaving a patch is a proportion of the light reaching the patch from all the other visible patches in the closed volume. Patch surface normals are typically distributed everywhere and some patches are occluded or partly obscured from each other. The accumulation of these radiation-attenuating effects is summed up as the form-factor between each pair of patches. The main and most time-consuming part of the radiosity calculation is the calculation of these form factors.
Model reduction of radiative heat transfer by a hierarchical radiosity method
Published in Numerical Heat Transfer, Part A: Applications, 2023
Mickaël Le Bohec, Denis Lemonnier, Didier Saury
In graphic rendering, from where the method is derived, the quantity of interest is the radiosity, which determines the color of a lightened object. In heat transfer problems, radiosity but also net heat flux are sought depending on the situation. It is observed that the latter converges more slowly than the former and, therefore, needs more view factors to be calculated.