While the diffuse and specular reflections we see on the surface of objects are two different visual results that come from the same basic operation of light, transmittance by contrast, is an effect created by pretty much the opposite process. Here, rather than bouncing off the surface of an object, light is allowed to pass into its volume. As with light bounce, this process can also produce a variety of material looks.
Describing an object as being transmissive, though, only tells us that it is allowing at least some of the light energy striking it to pass into the object's volume. From that point onwards, other properties of the object's physical makeup will come into play, determining just what happens to the light once it is inside the volume and so ultimately creating the final visual appearance of the object.
For instance, with glass, which in most situations is a highly transmissive substance, the light...