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

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

We have presented a physically-based rendering system that is accurate enough, general enough, and practical enough for the vast majority of lighting design and architectural applications. The simulation uses a light-backwards ray-tracing method with extensions to handle specular, diffuse and directional-diffuse reflection and transmission in any combination to any level in any environment. Not currently included in the calculation are participating media, diffraction and interference, phosphorescence, and polarization effects. There is nothing fundamental preventing us from modeling these processes, but so far there has been little demand for them from our users.

The principle users of Radiance are researchers and educators in public and private institutions, and lighting specialists at large architectural, engineering and manufacturing firms. There are between 100 and 200 active users in the U.S. and Canada, and about half as many overseas. This community is continually growing, and as the Radiance interface and documentation improves, the growth rate is likely to increase.

For the graphics research community, we hope that Radiance will provide a basis for evaluating new physically-based rendering techniques. To this end, we provide both the software source code and a set of precomputed test cases on our ftp server. The test suite includes diffuse and specular surfaces configured in a simple rectangular space with and without obstructions. More complicated models are also provided in object libraries and complete scene descriptions.

6. Acknowledgements

7. Software Availability

8. Bibliography

9. Appendix