Great progress has been made over the last two decades in the simulation of photon transport within vegetation canopies using radiosity or ray tracing models. At the leaf scale, similarly, it is possible to track a single photon from cell to cell and to derive the optical properties of the entire blade by following the paths of hundreds, thousands, or even millions of photons (see Section 8.2.5). Ray tracing techniques require a detailed description of leaf geometrical properties, as well as knowledge of the mechanisms involved in the scattering and absorption of light at different levels of organization from organelle to leaf and at different wavelengths.