Design Nomenclature / Surface & Material
Transmission
Also called refraction, transmissive, specular transmission
The fraction of light passing through a material rather than reflecting or being absorbed, bent by the IOR on entry and exit. Unlike opacity, transmitted rays refract, tint by Beer–Lambert absorption over the distance travelled, and can focus into caustics. Thin-walled variants skip the refraction, which is how window glass renders cheaply.
Not to be confused with
- OpacityHow much a surface blocks light passing through it, stored per texel or set per material. A compositing quantity rather than a physical one: it blends the surface over what lies behind without refracting, tinting by path length, or conserving energy. Real glass is transmission; opacity is a stencil that happens to look like glass.
- TranslucencyTransmission with scattering: light passes through but its direction is randomized on the way, so the material glows without carrying an image. Frosted glass, vellum, thin marble, a paper lampshade. What survives is brightness and color; what does not is anything you could focus or read.
- ClearcoatA second specular lobe layered over the base material to stand in for a transparent coating — car paint, lacquered wood, wet plastic. It carries its own roughness and a fixed IOR near 1.5. Its thickness control only tints by absorption; the layer has no simulated depth and no parallax.