Radiance
Highly accurate ray-tracing software system for UNIX computers
...Scene geometry, materials, luminaires, time, date and sky conditions (for daylight calculations) are specified; spectral radiance (ie. luminance + color), irradiance (illuminance + color) and glare indices are calculated. Simulation results may be displayed as color images, numerical values and contour plots.
Radiance is useful for architects and engineers in predicting illumination, visual quality and appearance of innovative design spaces; and for researchers in evaluating new lighting and daylighting technologies.