lighttransport

Light transport is the study of how light energy propagates and distributes itself through media and across interfaces. It encompasses absorption, scattering, reflection, refraction, and emission, and it applies to both participating media, such as fog, tissue, or water, and non-participating surfaces. The goal is to predict quantities like radiance, irradiance, and flux at given locations and directions.

The radiative transfer equation (RTE) is the foundational model of light transport. It describes the change in radiance along a line of sight due to absorption and out-scattering, as well as in-scattering from other directions and any local emission. The equation depends on optical properties such as the absorption coefficient, scattering coefficient, and the phase function that characterizes how scattering redirects light. The anisotropy factor g and the refractive index are also important, especially at boundaries where Fresnel reflections occur.

Solutions to the RTE range from analytic results in simple geometries to approximations and numerical methods. The diffusion approximation simplifies the RTE for highly scattering, optically thick media. Monte Carlo methods simulate many photon paths to estimate radiance in complex scenes or tissues. Wave-optics effects and coherence can be important in some regimes, requiring more detailed models beyond classical transport.

In computer graphics and vision, light transport is solved to achieve realistic rendering or imaging. Techniques include path tracing, bidirectional path tracing, photon mapping, and radiosity, all aimed at capturing global illumination by accounting for multiple light–surface interactions.

Applications span atmospheric and astrophysical radiative transfer, underwater optics, and biomedical imaging such as diffuse optical tomography and optical coherence tomography. Key concepts include radiance, albedo, optical depth, and boundary conditions at material interfaces.