Physically Based Rendering is a recent approach to texturing and rendering that focuses on creating materials which accurately represent real-world materials. PBR materials interact realistically with the surroundings and different lighting conditions to produce a result that mimics real-world surfaces.
PBR employs the use of specular reflection, translucency energy conservation and Fresnel, metals and microsurface which are described in detail below.
Specular and Diffuse reflection
When light hits a surface, there are two basic surface/light interaction outcomes. In the situation of specular reflection, light immediately bounces off a surface, like a ball being thrown against the ground. The result is a mirror-like reflection of the environment of a varying blurriness, depending on the roughness of the surface.
Diffuse reflection is when light enters through the surface of an object where some of it will either be absorbed or scattered internally. The light that emerges back is distributed randomly into the environment and depending on the wavelength of the light, produces different colors.
Energy Conversation
This refers to a real-life law which dictates that the light leaving a surface after it has penetrated it can never be brighter than the initial light. Basically, more light cannot be reflected by a surface than was initially received. This also means that reflection and diffusion are mutually exclusive so for example, very reflective surfaces will have very little or no diffuse light since most of the light has been reflected. Using these principles in PBR allows the artist to produce materials that do not violate the laws of physics.
References
Lola Koha 