Currently, the primary method for modelling light fields in lighting installations relies on Monte Carlo techniques. However, the conventional direct Monte Carlo approach has significant limitations. A promising solution to these shortcomings lies in local estimation methods, initially developed for radiative transfer problems.
This paper presents a formulation of initial and transitional ray-wandering densities within a scene, enabling local estimation of luminance as well as any other integral light-field characteristic expressible as a linear functional of luminance and a radiation value function defined by the corresponding receiver. By employing an orthonormal basis for this function, the method is extended to optical system modelling in luminaires.
Building on these developments and prior research, the authors propose a universal light-field modelling method applicable to three key areas in lighting practice:
 Optical system simulation,
 Multiple reflection calculations, and
 Light-surface interaction modelling.
The method has been implemented in Light-in-Night, a newly developed simulation program. Its results have been benchmarked against comparable software tools.
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• ray tracing
• photon maps
• local estimations
• Monte Carlo method
• optical systems
• multiple reflections