The RADIANCE Lighting Simulation and Rendering System

Gregory J. Ward /


1. Introduction

2. System Design Goals

2.1 Ensure Accurate Calculation of Luminance

2.2 Model Both Electric Light and Daylight

2.3 Support a Variety of Reflectance Models

2.4 Support Complicated Geometry

A lighting simulation of an empty room is not very interesting, nor is it very informative. The contents of a room must be included if light transfer is to be calculated correctly. Also, it is difficult for humans to evaluate aesthetics based on visualizations of empty spaces. Furniture, shadows and other details provide the visual cues a person needs to understand the lighting of a space. Modeling exteriors is even more challenging, often requiring hundreds of thousands of surfaces.

Although we leave the definition of "complicated geometry" somewhat loose, including it as a goal means that we shall not limit the geometric modeling capability of our simulation in any fundamental way. To be practical, data structure size should grow linearly (at worst) with geometric complexity, and there should be no built-in limit as to the number of surfaces. To be accurate, we shall support a variety of surface primitives, also ensuring our models are as memory-efficient as possible. To be general, we shall provide N-sided polygons and a mechanism for interpolating surface normals, so any reasonable shape may be represented. Finally, computation time should have a sublinear relationship to the number of surfaces so that the user does not pay an unreasonable price for accurate modeling.

2.5 Take Unmodified Input from CAD Systems

3. Approach

3.1 Hybrid Deterministic/Stochastic Ray Tracing

3.2 Cached Indirect Irradiances for Diffuse Interreflection

3.3 Adaptive Sampling of Light Sources

3.4 Automatic Preprocessing of "Virtual" Light Sources

3.5 User-directed Preprocessing of "Secondary" Sources

3.6 Hierarchical Octrees for Spatial Subdivision

3.7 Patterns and Textures

3.8 Parallel Processing

3.9 Animation

3.10 Implementation Issues

4. Applications and Results

4.1 Electric Lighting

4.2 Daylighting

5. Conclusion

6. Acknowledgements

7. Software Availability

8. Appendix