Recently, much more lighting simulation tools or 3DCAD/CG tools implement algorithms for lighting environment simulation. However, some users of these tools do not understand how the algorithms work and, consequently, they do not know appropriate algorithm for a certain case study. To simulate lighting environment taking into account interreflection, boundary condition of architectural space or light flux must be considered discretely to keep computational load finite. In this article, author try to describe brief explanation of radiosity method, which transacts continuous boundary condition discretely, and raytracing method, which transacts infinite light flux discretely, so that even beginners of numeric calculation can comprehend both algorithms intuitively. At first, principle of interreflection calculation is explained with simple case with 2 elements. Then, calculation method of incident luminous flux ratio from another element is described. Finally, advantageous points and disadvantageous points of both algorithms are explained with various example figures of calculation result.
One of the ultimate goals of computer graphics is to create realistic virtual environments. Rendering realistic images of the virtual environments is a key element to achieve this goal. In order to synthesize realistic images, we need to accurately simulate interactions of light with virtual objects while taking into account interreflections of light or global illumination effects. Global illumination is the major research topic in computer graphics and has a long research history. In early days, global illumination was simulated under simplified assumptions such as diffuse surfaces only. However, recent advancement in computer performance makes us possible to handle much more general situations, such as specular/transparent surfaces or moving objects, and many methods have been proposed. These methods can be classified into two approaches; precomputation-based or precomputation-free approaches. In this article, we will review several methods for these two approaches and discuss the future of the researches on the realistic images synthesis.
Test cases to assess the accuracy of lighting simulation programes were proposed in the CIE 171:2006. Five fundamental cases were extracted and summarized in this article, and the accuracy of four programes - Dialux, Lumicept, Radiance, 3ds Max - was verified with these cases. Test case 1 & 2 are to inspect the accuracy based on the measurement data. For point illuminance measurements, the reference values are presented by means of two pairs of upper and lower limits, where the first pair defines a band of values including the measurement errors and the second pair defines a band including both measurement and simulation errors. Test case 3 & 4 & 5 are to compare simulation values with analytically calculated data. Test case 3 check the accuracy of direct illuminance by artificial point light sources, test case 4 check the accuracy of direct illuminance by artificial area light sources, and test case 5 check the inter-reflections. As to test case 1 & 2 & 3, all programes get satisfactory results for the most part.
The outline of the utilization of the lighting simulation program is reported. Specifically, questionnaire survey for lighting designers was performed and the situation of utilization of the lighting simulation program in a real project, the outputs that the designer is going to get from the lighting simulation, the reasons why the designers don't conduct lighting simulation, the share of the lighting simulation software and the demands for the lighting simulation program by the designers are reported.