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

Electric lighting was the first domain of Radiance, and it continues to be a major strength. A model may contain any number of light sources of all shapes and sizes, and the output distributions may be entered as either near-field or far-field data. The dual nature of light sources (mentioned in section 3.5) also permits detailed modeling of fixture geometry, which is often important in making aesthetic decisions.

There are several application areas where electric lighting is emphasized. The most obvious application is lighting design. Figure 13 shows a comparative study between three possible lighting alternatives in a hotel lobby space. Several other designs were examined in this exploration of design visualization. With such a presentation, the final decision could be safely left to the client.

One design application that requires very careful analysis is indirect lighting. Figure 14 shows a simulation of a new control center for the London Underground. The unusual arrangement of upwardly directed linear fluorescents was designed to provide general lighting without affecting the visibility of the central display panel (image left).

Stage lighting is another good application of physically-based rendering. The designs tend to be complex and changing, and the results must be evaluated aesthetically (i.e. visually). Figure 15 shows a simulation of a scene from the play Julius Caesar. Note the complex shadows cast by the many struts in the stage set. Computing these shadows with a radiosity algorithm would be extremely difficult.

4.2 Daylighting

5. Conclusion

6. Acknowledgements

7. Software Availability

8. Bibliography

9. Appendix