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

Luminance is a directional quantity, and its value is strongly determined by a material's reflectance/transmittance distribution function. If luminance is calculated using a Lambertian (i.e. diffuse) assumption, specular highlights and reflections are ignored and the result can easily be wrong by a hundred times or more. We cannot afford to lose directional information if we hope to use our simulation to evaluate visual performance, visual comfort and aesthetics.

A global illumination program is only as general as its local illumination model. The standard model of ambient plus diffuse plus Phong specular is not good enough for realistic image synthesis. Radiance includes the ability to model arbitrary reflectance and transmittance functions, and we have also taken empirical measurements of materials and modeled them successfully in our system [29].

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

6. Acknowledgements

7. Software Availability

8. Bibliography

9. Appendix