Physically based shading is similar to shading as we used to do before, but now the lighting calculations are based on the physics of light with some precision. Correctness is defined as realistic behavior. You can check if the lighting implemented in your shader is correct by rendering the same scene using a physically based offline renderer.
This chapter discusses the principles of the physics of light that are interesting to us. We presented some information about the behavior of light when hitting a surface in Chapter ...
