Energy Conservation

From Tech Artists Wiki

Energy Conservation is a law of energy, that states the total amount of energy in an isolated system remains constant, but can change forms. This is most relevant in computer graphics with its application to lighting.

When a ray of light of a certain intensity hits a surface, the direct light does one of three things: it diffuses, reflects (specular), or is absorbed (sub-surface scattering). In theory, the sum of energy from these three components should be equal to the energy of the light coming in.

Rather than use these physical properties to mathematically calculate light based on formulaic material properties, it is much easier to use this information when creating any texture or shader. The high reflectivity of metals means that they have a lower diffuse component (a perfectly reflective metal, like chrome, has no diffuse component), and a surface that is of a certain roughness will be perfectly diffusely lit, with no reflectance. The rendering of direct lighting can be made more nuanced and believable by understanding these physical laws.