Important Materials Theory - Photographic Rendering with V-Ray for SketchUp - page 260

The importance of energy-conserving
materials
Fortunately for us (given all of these complex processes taking place), the one thing
that we don't have to worry about when using either the Standard or V-Ray Materi-
als is the need to balance out the various reflectance, transmittance, and reflectivity
properties as both of these materials handle incoming and outgoing light energy in
a physically accurate manner, which means that they can correctly be referred to as
energy-conserving materials.
In the bad old days of computer graphics, before render engines like V-Ray came
along, materials relied on the good judgment of the artist in order to create a good
looking balance between diffuse and specular components, which unfortunately
(without a decent grounding in the physics of light) is not quite as easy to do as it may
at first sound. This is why many renders produced in the 1990s suffered from what
came to be referred to as the CG look.
Note
It does need to be said that unrealistic materials were not the sole contributors to
this particular look. A lack of usable global illumination tools, inaccurate lighting
setups, and other elements certainly contributed greatly to the unrealistic look of
many 3D renders at the time.
The problem that shader or material writers were wrestling with back then was the fact
that light only strikes a surface with a finite amount of energy, which then of course
has to be accurately disposed of in accordance with the type of surface it is supposed
to be. So a material cannot realistically be set up so that it has 50 percent diffuse re-
flectance, 50 percent specular reflectivity, and at the same also be 50 percent trans-
missive or see-through. This would mean that from apparently nowhere, our light had
suddenly gained an extra 50 percent of incoming energy (3 x 50 equaling 150), which
of course breaks the laws of thermodynamics and so cannot, if a material is to be
realistic looking, be allowed to happen.
In general, physically correct energy distribution dictates the following points: