# About Radiance

Radiance is a suite of programs for the analysis and visualization of lighting in design.

Input files specify the scene geometry, materials, luminaires,time, date and sky conditions (for daylight calculations). Calculated values include spectral radiance (ie. luminance + color), irradiance (illuminance + color) and glare indices. Simulation results may be displayed as color images, numerical values and contour plots.

The primary advantage of Radiance over simpler lighting calculation and rendering tools is that there are few limitations on the geometry or the materials that may be simulated. Radiance is used by architects and engineers to predict illumination, visual quality and appearance of innovative design spaces, and by researchers to evaluate new lighting and daylighting technologies.

### Radiance Specifications:

Modeling and Simulation Capabilities | |
---|---|

Geometry | Planar polygons, planar rings, triangulated meshes, spheres, cylinders, cones. "Source - spherical solid angle for skies. |

Light model | Inverse square trichromatic with adaptive area subdivision |

Color model | Radiometric RGB or (for specialized versions) XYZ. Radiance RGB primaries are close to, but predate, the sRGB primaries |

Shaders | Ward empirical shader, procedural and data-based BRTDF shader |

Reflection and refraction | Mirrors, prismatic glazing, dielectric interfaces |

Opaque and translucent materials | Parameterized by the Ward shader, based on measurable material properties |

Transport materials | Extensive support for glazing. Thin glass and arbitrarily layered transparent materials are supported |

Surface maps | Procedural and data-based visual textures ("patterns") and bump maps ("textures") |

Mist, smoke, and clouds | Single-scattering. |

Complex light sources | Pre-computed light distributions through large areas of glazing. Luminaire geometry can be "wrapped" with an invisible light-radiating surface to provide luminaries with accurate photometry. |

Input/Output | |

Geometry input | Textual; usually via conversion from CAD file format, but can be directly written of generated by scripts or provided geometry generators. |

Materials input | Textual |

Graphical output | Via RGBE HDR image files, the original HDR file format |

Simulation Methods | |

Rendering method | Hybrid deterministic/stochastic (Monte Carlo) ray tracing. Direct illumination and specular reflections are calculated deterministically. Indirect diffuse contributions and their gradients are calculated at a carefully-chosen subset of surface points, used to estimate neighboring values, and cached. Various other heuristics are used to accelerate the calculation. |

Ray intersection finding algorithm | Octree spatial subdivision. Intersection-finding time has been measured to grow at slightly less than the fourth root of the number of surfaces in a scene. |

Parallelization | Indirect diffuse contributions are accumulated and shared among local or distributed ray-tracing processes. |

Animation | Z-buffer acceleration and indirect diffuse contribution sharing. |