RADIANCE is a physically-based lighting simulation program developed by Lawrence Berkeley National Laboratories in the US. It is used for the simulation and analysis of both natural and artificial lighting environments. The program takes a scene description - including light sources, sun position, sky type, buildings, rooms and furnishings - and produces spectral radiance values represented as 'photo-accurate' high resolution colour images. These images can then be post-processed to yield highly accurate images and contour maps of lighting values - clearly showing Lux levels. For more information, visit the Radiance Home Page.
Development of this tool was funded by US National Energy Agencies with a bias toward energy saving applications. Therefore, simulation of daylighting is very strong. Radiosity-based diffuse reflection calculations make it suitable for the analysis of indirect lighting systems such as light shelves. Elements such as prismatic glazing can be modelled through custom primitive types. Advanced surface reflectance models can be applied to correctly account for both diffuse and specular inter-reflection within complex spaces. Artificial lighting is modelled through photometric data which is fitting-specific and supplied directly by the manufacturer.
Post-processing of results provides graphical and numerical data for relating luminance, illuminance, colour renderings, visual comfort and glare indices. An example image showing the level of complexity possible is shown in Figures 1 and 2 below.