Important Materials Theory - Photographic Rendering with V-Ray for SketchUp - page 239

How absorption, reflectance, and

transmittance work

In fact, for the purpose of this simplified discussion, we could say that one of three
things, will occur at that point. Our light (or parts of it at least) will either be absorbed,
reflected, or transmitted (that is, pass through) the object it is falling on. To use the
technical parlance, we will see absorption, reflectance, and transmittance or maybe a
combination of two or more of these occur. Exactly how these combinations work will
depend entirely upon the physical properties of the material/object that the white light
is striking.

• Absorption : This is what happens when the substance from which an object
is made holds onto or absorbs certain component wavelengths of the light
striking it. In the case of a black or nearly black object for instance, pretty much
all of the light wavelengths are being absorbed, and so what we are left with
is (quite literally) an absence of diffuse light reflection. You will have probably
noticed that many black objects only have a recognizable shape or a defined
outline because the materials from which they are made also have what we
call reflective properties.

• Diffuse Reflection ( Reflectance ): This is really the exact opposite of absorp-
tion in that it profiles the light wavelengths that are being reflected off a sur-
face and so producing a visible surface color. The reflectance value for a
given surface is used to describe the energy or strength with which various