Global Illumination

Ray tracing is often considered superior to rasterisation because it belongs to the family of lighting models known as global illumination. Rasterisation, on the other hand, uses a local illumination model.

However, global illumination by itself doesn't ensure good lighting. It's also necessary to have global illumination data to solve the Kajiya rendering equation, but it doesn't ensure that the results will be any good. Most renderers are simplifications of the Kajiya equation, dropping or simplifying terms that are too expensive to compute.

Ray tracing is a solution to the direct lighting portion of the equation and traditionally replaces the indirect lighting portion with a local illumination model. So the idea that it's a physically correct lighting solution is wrong; the tracing of rays is often used in better physically correct global illumination models, but these aren't themselves ray tracing.

This means ray tracing can solve the lighting of very directly lit and shiny scenes fairly well, but the quality of more diffuse scenes is not great. The basic models using point light sources also produce hard shadows, and a move to area lights produces nice soft shadows but means many more rays to trace.

Trying to capture indirect lighting via firing additional rays doesn't work very well, and has been abandoned in the off-line rendering world, with techniques such as photon tracing being used in its stead.